This CL is a nightmare! For the utterly irrelevant edge case of a sloppy function with non-simple parameters and a call to direct eval, like here,
let x = 1;
function f(g = () => x) {
var y
eval("var x = 2")
return g() + x // f() = 3
}
we have to do all of the following, on top of the declaration block ("varblock") contexts we already introduce around the body:
- Introduce the ability for varblock contexts to have both a ScopeInfo and an extension object (e.g., the body varblock in the example will contain both a static var y and a dynamic var x). No other scope needs that. Since there are no context slots left, a special new struct is introduced that pairs up scope info and extension object.
- When declaring lookup slots in the runtime, this new struct is allocated in the case where an extension object has to be added to a block scope (at which point the block's extension slot still contains a plain ScopeInfo).
- While at it, introduce some abstraction to access context extension slots in a more controlled manner, in order to keep special-casing to a minimum.
- Make sure that even empty varblock contexts do not get optimised away when they contain a sloppy eval, so that they can host the potential extension object.
- Extend dynamic search for declaration contexts (used by sloppy direct eval) to recognize varblock contexts.
- In the parser, if a function has a sloppy direct eval, introduce an additional varblock scope around each non-simple (desugared) parameter, as required by the spec to contain possible dynamic var bindings.
- In the pattern rewriter, add the ability to hoist the named variables the pattern declares to an outer scope. That is required because the actual destructuring has to be evaluated inside the protecting varblock scope, but the bindings that the desugaring introduces are in the outer scope.
- ScopeInfos need to save the information whether a block is a varblock, to make sloppy eval calls work correctly that deserialise them as part of the scope chain.
- Add the ability to materialize block scopes with extension objects in the debugger. Likewise, enable setting extension variables in block scopes via the debugger interface.
- While at it, refactor and unify some respective code in the debugger.
Sorry, this CL is large. I could try to split it up, but everything is rather entangled.
@mstarzinger: Please review the changes to contexts.
@yangguo: Please have a look at the debugger stuff.
R=littledan@chromium.org, mstarzinger@chromium.org, yangguo@chromium.org
BUG=v8:811,v8:2160
LOG=N
Review URL: https://codereview.chromium.org/1292753007
Cr-Commit-Position: refs/heads/master@{#30295}
* Add types to properly report what has been executed in the GC
* Unify GCPrologueCallback and GCEpilogueCallback into GCCallback
* Report processing of second round weak handels, either synchronously or asynchronously
BUG=chromium:521946
LOG=N
Review URL: https://codereview.chromium.org/1298113003
Cr-Commit-Position: refs/heads/master@{#30218}
- Make the API look like v8::V8::InitializeICU.
(That is: A static method call, not an object to be created on the stack.)
- Fix path separator on Windows, by calling base::OS::isPathSeparator.
- Move into API, so that it can be called by hello-world & friends.
- Actually call it from hello-world and friends.
R=jochen@chromium.org
BUG=
Review URL: https://codereview.chromium.org/1292053002
Cr-Commit-Position: refs/heads/master@{#30174}
Improves on aec8987b5e by not forcing external GCs
(blink) through the GC epilogue callback.
BUG=chromium:515795
LOG=N
Review URL: https://codereview.chromium.org/1287323002
Cr-Commit-Position: refs/heads/master@{#30164}
First step to simplify the TypeofStub. This is similar to the
optimization that we use for ToNumber and ToString on Oddballs already.
R=yangguo@chromium.org
Review URL: https://codereview.chromium.org/1272763005
Cr-Commit-Position: refs/heads/master@{#30108}
There's no need to have one InstanceType per SIMD primitive type (this
will not scale long-term). Also reduce the amount of code duplication
and make it more robust wrt adding new SIMD types.
R=yangguo@chromium.org
Review URL: https://codereview.chromium.org/1273353003
Cr-Commit-Position: refs/heads/master@{#30107}
No need to provide TO_INT32/TO_UINT32 functions for every native
context, as they can be implemented in terms of TO_NUMBER more easily
and efficiently.
Also remove the obsolete TO_BOOLEAN_FUN_INDEX from the native contexts.
Review URL: https://codereview.chromium.org/1275013004
Cr-Commit-Position: refs/heads/master@{#30080}
This is only an estimate since it counts objects that could be shared,
for example strings, cow arrays, heap numbers, etc.
It however ignores objects that could be shared, but may only be used
by the context to be measured, for example shared function infos,
script objects, scope infos, etc.
R=jochen@chromium.org
Review URL: https://codereview.chromium.org/1268333004
Cr-Commit-Position: refs/heads/master@{#30029}
There is only one use case for it: String.prototype.search converts a
string argument into a RegExp. The cache is used to avoid repeating that
conversion. However, this does not make the added complexity worthwhile.
Review URL: https://codereview.chromium.org/1267493006
Cr-Commit-Position: refs/heads/master@{#29985}
This is the initial (big) step towards a more uniform implementation of
the ToObject abstract operation (ES6 7.1.13), where we have a fallback
implementation in JSReceiver::ToObject() and a fast (hydrogen) CodeStub
to deal with the fast case (we should be able to do more cleanup on this
in a followup CL). For natives we expose the abstract operation via a
%_ToObject intrinsic, also exposed via a macro TO_OBJECT, that unifies
the previous confusion with TO_OBJECT_INLINE, ToObject, TO_OBJECT,
$toObject and %$toObject. Now the whole implementation of the abstract
operation is context independent, meaning we don't need any magic in the
builtins object nor the native context.
R=mvstanton@chromium.org,yangguo@chromium.org
Review URL: https://codereview.chromium.org/1266013006
Cr-Commit-Position: refs/heads/master@{#29953}
This is required in order for Globals to be stored in STL containers.
Patch from Aaron Link <aaronlink@google.com>
BUG=
Review URL: https://codereview.chromium.org/1244033002
Cr-Commit-Position: refs/heads/master@{#29776}
This CL exposes the constructor function, defines type related
information, and implements value type semantics.
It also refactors test/mjsunit/samevalue.js to test SameValue and SameValueZero.
TEST=test/mjsunit/harmony/simd.js, test/cctest/test-simd.cc
LOG=Y
BUG=v8:4124
Committed: https://crrev.com/e5ed3bee99807c502fa7d7a367ec401e16d3f773
Cr-Commit-Position: refs/heads/master@{#29689}
Review URL: https://codereview.chromium.org/1219943002
Cr-Commit-Position: refs/heads/master@{#29712}
These were added when I thought they would be useful in Blink, but as
it turned out they were not. They could likely be deleted immediately,
but to play it safe I'll go through the usual deprecation process.
Review URL: https://codereview.chromium.org/1236263004
Cr-Commit-Position: refs/heads/master@{#29690}
This CL exposes the constructor function, defines type related
information, and implements value type semantics.
It also refactors test/mjsunit/samevalue.js to test SameValue and SameValueZero.
TEST=test/mjsunit/harmony/simd.js, test/cctest/test-simd.cc
LOG=Y
BUG=v8:4124
Review URL: https://codereview.chromium.org/1219943002
Cr-Commit-Position: refs/heads/master@{#29689}
The CL addes convenienve method that allows to write code like the following
v8::Local<v8::Object> local = v8::Local<v8::Object>::New(global, isolate);
in a more readable way:
v8::Local<v8::Object> local = global.Get(isolate);
There is already v8::Eternal::Get that does similar thing.
BUG=None
LOG=Y
Review URL: https://codereview.chromium.org/1237603003
Cr-Commit-Position: refs/heads/master@{#29616}
The only right way to enable access checks is to install access check callbacks on an object template via v8::ObjectTemplate::SetAccessCheckCallbacks(). It does not make sense to enable access checks on an arbitrary object.
Review URL: https://codereview.chromium.org/1217893012
Cr-Commit-Position: refs/heads/master@{#29439}
Map: get, set, has, delete, clear
Set: add, has, delete, clear
All except clear are implemented as calls into collection.js.
Note that some of these shadow methods of v8::Object. It's unclear
how confusing that's going to be: on the one hand, it seems likely
that most operations you would want to do on a Map or Set are these.
On the other, generic code could get confused if it somehow gets
ahold of a variable that happens to be C++-typed as a v8::Map or v8::Set.
BUG=v8:3340
LOG=y
Review URL: https://codereview.chromium.org/1204623002
Cr-Commit-Position: refs/heads/master@{#29237}
Delayed tasks can be used to perform non-urgent clean up work.
BUG=chromium:490559
LOG=NO
Review URL: https://codereview.chromium.org/1179153002
Cr-Commit-Position: refs/heads/master@{#29084}
Up until now we used int32_t for NodeId, but that was not ideal because
negative values are invalid for NodeId and we use it as an array index
for example in the NodeMarker class, where C++ compilers on x64 have to
generate code that does proper sign extension for the indices, which is
completely unnecessary.
R=svenpanne@chromium.org
Review URL: https://codereview.chromium.org/1178403004
Cr-Commit-Position: refs/heads/master@{#28997}
Embed constant pools within their corresponding Code
objects.
This removes support for out-of-line constant pools in favor
of the new approach -- the main advantage being that it
eliminates the need to allocate and manage separate constant
pool array objects.
Currently supported on PPC and ARM. Enabled by default on
PPC only.
This yields a 6% improvment in Octane on PPC64.
R=bmeurer@chromium.org, rmcilroy@chromium.org, michael_dawson@ca.ibm.com
BUG=chromium:478811
LOG=Y
Review URL: https://codereview.chromium.org/1162993006
Cr-Commit-Position: refs/heads/master@{#28801}
This will significantly simplify the serialization code, as well
as speeding it up (by triggering only a single allocation instead of O(size)
allocations).
BUG=chromium:478263
LOG=y
Review URL: https://codereview.chromium.org/1157843006
Cr-Commit-Position: refs/heads/master@{#28793}
These are similar to the Map/Set constructors when called with an array,
except that they are guaranteed to be side-effect free if called with
a packed array.
This will be useful in implementing structured clone which, as
specified in HTML, speaks in terms of the internal [[MapData]]
and [[SetData]] slots without going through the exposed iteration
ES semantics.
BUG=v8:3340
LOG=y
Review URL: https://codereview.chromium.org/1155893003
Cr-Commit-Position: refs/heads/master@{#28642}
These return arrays representing the current contents of the given
Map/Set. They are similar to what would be returned by the JS code:
Array.from(collection)
except that they are guaranteed side-effect free.
This will be useful in implementing structured clone which, as
specified in HTML, speaks in terms of the internal [[MapData]]
and [[SetData]] slots without going through the exposed iteration
ES semantics.
BUG=v8:3340
LOG=y
Review URL: https://codereview.chromium.org/1148383007
Cr-Commit-Position: refs/heads/master@{#28640}
Only supports constructing new objects and returning size.
Followup patch will need to add ability to retrieve and
set contents in order to support structured clone.
Also removes a bunch of outdated "experimental" markers from v8.h.
BUG=v8:3340
LOG=y
Review URL: https://codereview.chromium.org/1157453002
Cr-Commit-Position: refs/heads/master@{#28637}
(Requires the embedder's ExternalSourceStream implementation to cooperate.
See crrev.com/1154883003 for Blink.)
R=jochen@chromium.org
BUG=chromium:470930
LOG=Y
Review URL: https://codereview.chromium.org/1156733002
Cr-Commit-Position: refs/heads/master@{#28610}
This adds a new external type (v8::SharedArrayBuffer) that uses a JSArrayBuffer
under the hood. It can be distinguished from an ArrayBuffer by the newly-added
is_shared() bit.
Currently there is no difference in functionality between a SharedArrayBuffer
and an ArrayBuffer. However, a future CL will add the Atomics API, which is
only available on an SharedArrayBuffer. All non-atomic accesses are identical
to ArrayBuffer accesses.
LOG=N
BUG=
Review URL: https://codereview.chromium.org/1136553006
Cr-Commit-Position: refs/heads/master@{#28594}
Reason for revert:
breaks build
Original issue's description:
> Implement SharedArrayBuffer.
>
> This adds a new external type (v8::SharedArrayBuffer) that uses a JSArrayBuffer under the hood. It can be distinguished from an ArrayBuffer by the newly-added is_shared() bit.
>
> Currently there is no difference in functionality between a SharedArrayBuffer and an ArrayBuffer. However, a future CL will add the Atomics API, which is only available on an SharedArrayBuffer. All non-atomic accesses are identical to ArrayBuffer accesses.
>
> BUG=
>
> Committed: https://crrev.com/57170bff7baf341c666252a7f6a49e9c08d51263
> Cr-Commit-Position: refs/heads/master@{#28588}
TBR=jarin@chromium.org,jochen@chromium.org,binji@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=
Review URL: https://codereview.chromium.org/1149203003
Cr-Commit-Position: refs/heads/master@{#28589}
This adds a new external type (v8::SharedArrayBuffer) that uses a JSArrayBuffer under the hood. It can be distinguished from an ArrayBuffer by the newly-added is_shared() bit.
Currently there is no difference in functionality between a SharedArrayBuffer and an ArrayBuffer. However, a future CL will add the Atomics API, which is only available on an SharedArrayBuffer. All non-atomic accesses are identical to ArrayBuffer accesses.
BUG=
Review URL: https://codereview.chromium.org/1136553006
Cr-Commit-Position: refs/heads/master@{#28588}
This macro is used for defining static data members with
STATIC_CONST_MEMBER_DEFINITION. Clang-cl mimics MSVC's
behaviour here, so it also needs __declspec(selectany).
This change was prompted by Clang r237787 which changed
a bug where Clang would previously not emit symbols for
some static data members.
BUG=82385
LOG=N
Review URL: https://codereview.chromium.org/1145213004
Cr-Commit-Position: refs/heads/master@{#28563}
This should help to keep syntax errors from creeping into v8.h
Also, I'll remove usages of to-be-deprecated APIs and turn this flag on
for standalone builds
BUG=4134
R=vogelheim@chromium.org
LOG=n
Review URL: https://codereview.chromium.org/1149633003
Cr-Commit-Position: refs/heads/master@{#28538}
For dumping the number of objects and size of objects alive after the
last gc into chrome://tracing memory dumps, this CL adds new api to
get these number for each isolate.
Note: Chrome should be run with --js-flags='--track_gc_object_stats
--noincremental-marking' for object tracking.
BUG=476013
LOG=Y
Review URL: https://codereview.chromium.org/1113233002
Cr-Commit-Position: refs/heads/master@{#28474}
When the page is controlled by a ServiceWorker, the ServiceWorker can return an opaque (non-CORS cross origin) resource response.
We need to treat the messages from such script resource as opaque.
Committed: https://crrev.com/7a599c5e1242d3c5ab7515ee149623da90ae69ec
Cr-Commit-Position: refs/heads/master@{#28445}
Review URL: https://codereview.chromium.org/1140673002
Cr-Commit-Position: refs/heads/master@{#28459}
When the page is controlled by a ServiceWorker, the ServiceWorker can return an opaque (non-CORS cross origin) resource response.
We need to treat the messages from such script resource as opaque.
Review URL: https://codereview.chromium.org/1140673002
Cr-Commit-Position: refs/heads/master@{#28445}
Some of the DevTools' clients need to inspect JS objects without enabling debugger. This CL allows to inspect object's internal properties without enabling debugger and instantiating debug context.
Note that now debug context can be created lazily if v8::Debug::GetDebugContext is called when there is no debug listener. This is fragile and has already resulted in some subtle error. I'm going to fix that in a separate CL.
BUG=chromium:481845
LOG=Y
Review URL: https://codereview.chromium.org/1134193002
Cr-Commit-Position: refs/heads/master@{#28371}
Reason for revert:
GC mole issues: https://chromegw.corp.google.com/i/client.v8/builders/V8%20Linux%20-%20gcmole/builds/1950/steps/GCMole%20ia32/logs/stdio
Original issue's description:
> Provide accessor for object internal properties that doesn't require debugger to be active
>
> Some of the DevTools' clients need to inspect JS objects without enabling debugger. This CL allows to inspect object's internal properties without enabling debugger and instantiating debug context.
>
> Note that now debug context can be created lazily if v8::Debug::GetDebugContext is called when there is no debug listener. This is fragile and has already resulted in some subtle error. I'm going to fix that in a separate CL.
>
> BUG=chromium:481845
> LOG=Y
>
> Committed: https://crrev.com/bdeb0de88c8cf5f2c78f261b45314138f525110d
> Cr-Commit-Position: refs/heads/master@{#28362}
TBR=pfeldman@chromium.org,kozyatinskiy@chromium.org,yurys@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:481845
Review URL: https://codereview.chromium.org/1133243002
Cr-Commit-Position: refs/heads/master@{#28365}
Some of the DevTools' clients need to inspect JS objects without enabling debugger. This CL allows to inspect object's internal properties without enabling debugger and instantiating debug context.
Note that now debug context can be created lazily if v8::Debug::GetDebugContext is called when there is no debug listener. This is fragile and has already resulted in some subtle error. I'm going to fix that in a separate CL.
BUG=chromium:481845
LOG=Y
Review URL: https://codereview.chromium.org/1126103006
Cr-Commit-Position: refs/heads/master@{#28362}
If there had been no debug listener v8::Debug::GetDebugContext would have created new context and wouln't have kept reference to it. This way we may well end up with several debug contexts and disabled debugger.
As a side effect this change allows to efficiently distinguish debug context from blink contexts by simply comparing handles.
BUG=chromium:482290
LOG=Y
Review URL: https://codereview.chromium.org/1136733002
Cr-Commit-Position: refs/heads/master@{#28356}
Exposed to the extras as extrasExports (on the builtins object), on
which they can put things that should be accessible from C++. Exposed
to C++ through the V8 API as v8::Context::GetExtrasExportsObject().
Adding a test (in test-api.cc) required adding a simple extra,
test-extra.js, which we build into the standalone builds.
R=yangguo@chromium.org, jochen@chromium.org
BUG=
Review URL: https://codereview.chromium.org/1128113006
Cr-Commit-Position: refs/heads/master@{#28317}
I know the bug has been closed but this seems like a simple addition that may
be useful in other ways as well.
BUG=v8:2180
LOG=N
Review URL: https://codereview.chromium.org/1128553002
Cr-Commit-Position: refs/heads/master@{#28261}
These macros are not needed anymore, so there's no point in supporting
them.
Review URL: https://codereview.chromium.org/1123723003
Cr-Commit-Position: refs/heads/master@{#28214}
Just give internal ones an ArrayBuffer with a NULL backing store. This
simplifies the access checks a lot.
BUG=v8:3996
R=hpayer@chromium.org,verwaest@chromium.org
LOG=n
Review URL: https://codereview.chromium.org/1109353003
Cr-Commit-Position: refs/heads/master@{#28168}
We shouldn't have shared state between isolates by default. The embedder
is free to pass the same allocator to all isolates it creates.
BUG=none
R=dcarney@chromium.org
LOG=y
Review URL: https://codereview.chromium.org/1116633002
Cr-Commit-Position: refs/heads/master@{#28127}
For dumping memory statistics about v8 heap, we need the total
available size of the heap. This CL adds extra field in HeapStatistics
to return the available size.
BUG=476013
LOG=Y
Review URL: https://codereview.chromium.org/1104123002
Cr-Commit-Position: refs/heads/master@{#28100}
The embedder has to take appropriate steps to ensure that the
ArrayBuffer doesn't die while it's accessing the pointer, e.g. keep a
Local handle to it around
BUG=none
R=dslomov@chromium.org
LOG=y
Review URL: https://codereview.chromium.org/1095083002
Cr-Commit-Position: refs/heads/master@{#27942}
This class was added in crrev.com/1058253003 and missed V8_EXPORT in
definition.
BUG=466141, 476013
LOG=Y
Review URL: https://codereview.chromium.org/1090333002
Cr-Commit-Position: refs/heads/master@{#27926}
This is first step towards adding V8 heap statistics to the memory
tracing infrastructure. For being able to get useful memory number into
the memory dump, v8 needs to provide an external api needs to obtain
more information about the heap. So, this Cl extends the api to give
information about the memory allocated and used in the spaces.
BUG=466141, 476013
LOG=Y
Review URL: https://codereview.chromium.org/1058253003
Cr-Commit-Position: refs/heads/master@{#27919}
The embedder can control how many threads it wants to use via the
v8::Platform implementation. V8 internally doesn't spin up threads
anymore. If the embedder doesn't want to use any threads at all, it's
v8::Platform implementation must either run the background jobs on
the foreground thread, or the embedder should specify --predictable
BUG=none
R=yangguo@chromium.org
LOG=y
Review URL: https://codereview.chromium.org/1064723005
Cr-Commit-Position: refs/heads/master@{#27833}
As uClibc defines __GLIBC__ in an attempt to look like glibc, V8_LIBC_GLIBC
was true for uClibc as well. Checking for uClibc before glibc fixes this
and restores the correct behavior.
BUG=
Review URL: https://codereview.chromium.org/1066573005
Cr-Commit-Position: refs/heads/master@{#27806}
This allows the embedder to decide whether it's worthwhile to copy the
contents to avoid materializing a buffer.
BUG=v8:3996
R=dslomov@chromium.org,kbr@chromium.org
LOG=y
Review URL: https://codereview.chromium.org/1084513002
Cr-Commit-Position: refs/heads/master@{#27782}
When debugging Handle leaks in io.js we found it very convenient to be
able to Seal some specific (root in our case) scope to prevent Handle
allocations in it, and easily find leakage.
R=yangguo
BUG=
Review URL: https://codereview.chromium.org/1079713002
Cr-Commit-Position: refs/heads/master@{#27766}
gcc rejects the following snippet, clang rejects it in -std=c++11 mode:
namespace A { template<class T> class C {}; }
namespace B { template class A::C<int>; }
Indeed, the C++ standard says in 14.7.2p2 "An explicit instantiation shall
appear in an enclosing namespace of its template", so cl.exe is incorrect to
allow this.
Just move the instantiation out of the v8 namespace to fix. No intended
behavior change. Fixes building with clang-cl on Windows.
BUG=chromium:475643
LOG=N
TBR=svenpanne@chromium.org
Review URL: https://codereview.chromium.org/1073903002
Cr-Commit-Position: refs/heads/master@{#27721}
Reason for revert:
Causes test failures on ARM bots related to cells and write barriers.
Original issue's description:
> Merge cellspace into old pointer space
>
> BUG=
>
> Committed: https://crrev.com/4e7163ce05f135918205c7855ae60a48e5d46cc5
> Cr-Commit-Position: refs/heads/master@{#27707}
TBR=hpayer@chromium.org,balazs.kilvady@imgtec.com,yangguo@chromium.org,verwaest@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=
Review URL: https://codereview.chromium.org/1053243003
Cr-Commit-Position: refs/heads/master@{#27711}
Instead, please use v8::Isolate::RequestInterrupt to synchronize
to the main thread.
R=yurys@chromium.org
API=Removed v8::Debug::DebugBreakForCommand
LOG=Y
Review URL: https://codereview.chromium.org/1036863002
Cr-Commit-Position: refs/heads/master@{#27625}
The motivation is that we prefer to avoid creating internal properties, and we have a usable field on maps ("transitions", which is not used for prototype maps).
This CL also ensures the invariant that prototype maps are never shared, even if they are in dictionary mode.
Review URL: https://codereview.chromium.org/1033653002
Cr-Commit-Position: refs/heads/master@{#27617}
It triggers once per context that calls observe (or attempts to access
any observation metadata, e.g. through Object.getNotifier).
Review URL: https://codereview.chromium.org/1048213002
Cr-Commit-Position: refs/heads/master@{#27557}
Before this patch the embedder could assign timestamp to the last interval after calling GetHeapStats. This would be slightly different from the timstamps assigned by v8 internally and written into heap snapshot. This patch allow to avoid this small discrepancy by returning timestamp along with last heap stats update.
BUG=chromium:467222
LOG=Y
Review URL: https://codereview.chromium.org/1037803002
Cr-Commit-Position: refs/heads/master@{#27466}
If the Maybe is nothing or the MaybeLocal is empty, it means that the
API call either threw an exception or an exception was already pending.
In that case, the embedder needs to handle the exception or otherwise
react to the failed API call.
BUG=v8:3929
R=svenpanne@chromium.org
LOG=y
Review URL: https://codereview.chromium.org/1022803002
Cr-Commit-Position: refs/heads/master@{#27298}
Some native counters (e.g. KeyedLoadGenericSlow) are referenced from stubs that are generated very early in the Isolate lifecycle before v8::Isolate::New returns. Thus counter lookup callback also needs to be installed early prior to v8::internal::Isolate::Init call. Otherwise assembler will just assume that the counter is not enabled and produce no code from IncrementCounter - because address of the counter is not yet available.
Histogram related callbacks are moved for consistency to make them able to collect samples which occur at isolate initialization time.
BUG=
Review URL: https://codereview.chromium.org/1010233002
Cr-Commit-Position: refs/heads/master@{#27262}
