The motivation is to avoid bugs such as the one fixed in
https://chromium-review.googlesource.com/c/v8/v8/+/800270.
Bug: v8:7109
Change-Id: I82a55f4a78d289d00ae7bafe78b45d92bab07a6b
Reviewed-on: https://chromium-review.googlesource.com/800291
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49829}
This patch normalizes the casing of hexadecimal digits in escape
sequences of the form `\xNN` and integer literals of the form
`0xNNNN`.
Previously, the V8 code base used an inconsistent mixture of uppercase
and lowercase.
Google’s C++ style guide uses uppercase in its examples:
https://google.github.io/styleguide/cppguide.html#Non-ASCII_Characters
Moreover, uppercase letters more clearly stand out from the lowercase
`x` (or `u`) characters at the start, as well as lowercase letters
elsewhere in strings.
BUG=v8:7109
TBR=marja@chromium.org,titzer@chromium.org,mtrofin@chromium.org,mstarzinger@chromium.org,rossberg@chromium.org,yangguo@chromium.org,mlippautz@chromium.org
NOPRESUBMIT=true
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I790e21c25d96ad5d95c8229724eb45d2aa9e22d6
Reviewed-on: https://chromium-review.googlesource.com/804294
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49810}
Both of these features were shipped in Chrome 62.
Bug: v8:4545, v8:6172
Cq-Include-Trybots: master.tryserver.v8:v8_linux_noi18n_rel_ng
Change-Id: Ie00dcbeded7517a15696d4a78fcfbbf162919923
Reviewed-on: https://chromium-review.googlesource.com/775601
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49453}
The wasm memory deserialization didn't properly increment the object id, so
wouldn't work properly if the memory object (or its contained
SharedArrayBuffer) where included multiple times in the object.
Bug: v8:6895
Change-Id: I5c4c25bad2ec6152883c5a7321038aba1950480a
Reviewed-on: https://chromium-review.googlesource.com/721630
Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Ben Smith <binji@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48767}
Also remove last internal callers of the to-be-deprecated APIs.
Bug: v8:2487
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng;master.tryserver.v8:v8_linux_noi18n_rel_ng
Change-Id: Id72cf363eac86e4b4dbf7df83bdb848071260b90
Reviewed-on: https://chromium-review.googlesource.com/639326
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47690}
Compilation failure is result to overloaded-virtual warning
treated as error.
BUG=
Review-Url: https://codereview.chromium.org/2895923002
Cr-Commit-Position: refs/heads/master@{#45525}
One of the serializer fuzzers passes in random data to the deserializer,
which can then be used to deserialize a JSRegExp instance with random flag
contents. This can cause issues since the JSRegExp::Flag enum statically
contains kDotAll - but it is only valid to set kDotAll iff
FLAG_harmony_regexp_dotall is set.
This CL verifies deserialized flags before constructing the JSRegExp
and bails out if they are invalid.
R=jbroman@chromium.org,yangguo@chromium.org
BUG=chromium:719280
Review-Url: https://codereview.chromium.org/2870743004
Cr-Commit-Position: refs/heads/master@{#45222}
Reason for revert:
Temporarily disabled tests on chromium side (https://codereview.chromium.org/2764933002)
Original issue's description:
> Revert of [wasm] Transferrable modules (patchset #13 id:280001 of https://codereview.chromium.org/2748473004/ )
>
> Reason for revert:
> Breaks layout tests:
> https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/14312
>
> See https://github.com/v8/v8/wiki/Blink-layout-tests
>
> Original issue's description:
> > [wasm] Transferrable modules
> >
> > We want to restrict structured cloning in Chrome to:
> > - postMessage senders and receivers that are co-located
> > in the same process
> > - indexedDB (just https).
> >
> > For context, on the Chrome side, we will achieve the postMessage part
> > by using a mechanism similar to transferrables: the
> > SerializedScriptValue will have a list of wasm modules, separate from
> > the serialized data stream; and this list won't be copied cross
> > process boundaries. The IDB part is achieved by explicitly opting in
> > reading/writing to the serialization stream. To block attack vectors
> > in IPC cases, the default for deserialization will be to expect data
> > in the wasm transfers list.
> >
> > This change is the V8 side necessary to enabling this design. We
> > introduce TransferrableModule, an opaque datatype exposed to the
> > embedder. Internally, TransferrableModules are just serialized data,
> > because we don't have a better mechanism, at the moment, for
> > de-contextualizing/re-contextualizing wasm modules (wrt Isolate and
> > Context).
> >
> > The chrome defaults will be implemented in the
> > serialization/deserialization delegates on that side. For the v8 side
> > of things, in the absence of a serialization delegate, the V8
> > serializer will write to serialization stream. In the absence of a
> > deserialization delegate, the deserializer won't work. This asymmetry
> > is intentional - it communicates to the embedder the need to make a
> > policy decision, otherwise wasm serialization/deserialization won't
> > work "out of the box".
> >
> > BUG=v8:6079
> >
> > Review-Url: https://codereview.chromium.org/2748473004
> > Cr-Commit-Position: refs/heads/master@{#43955}
> > Committed: 99743ad460
>
> TBR=jbroman@chromium.org,bradnelson@chromium.org,mtrofin@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=v8:6079
>
> Review-Url: https://codereview.chromium.org/2762163002
> Cr-Commit-Position: refs/heads/master@{#43981}
> Committed: e538b70e1aTBR=jbroman@chromium.org,bradnelson@chromium.org,machenbach@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:6079
Review-Url: https://codereview.chromium.org/2762273002
Cr-Commit-Position: refs/heads/master@{#43994}
Reason for revert:
Breaks layout tests:
https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/14312
See https://github.com/v8/v8/wiki/Blink-layout-tests
Original issue's description:
> [wasm] Transferrable modules
>
> We want to restrict structured cloning in Chrome to:
> - postMessage senders and receivers that are co-located
> in the same process
> - indexedDB (just https).
>
> For context, on the Chrome side, we will achieve the postMessage part
> by using a mechanism similar to transferrables: the
> SerializedScriptValue will have a list of wasm modules, separate from
> the serialized data stream; and this list won't be copied cross
> process boundaries. The IDB part is achieved by explicitly opting in
> reading/writing to the serialization stream. To block attack vectors
> in IPC cases, the default for deserialization will be to expect data
> in the wasm transfers list.
>
> This change is the V8 side necessary to enabling this design. We
> introduce TransferrableModule, an opaque datatype exposed to the
> embedder. Internally, TransferrableModules are just serialized data,
> because we don't have a better mechanism, at the moment, for
> de-contextualizing/re-contextualizing wasm modules (wrt Isolate and
> Context).
>
> The chrome defaults will be implemented in the
> serialization/deserialization delegates on that side. For the v8 side
> of things, in the absence of a serialization delegate, the V8
> serializer will write to serialization stream. In the absence of a
> deserialization delegate, the deserializer won't work. This asymmetry
> is intentional - it communicates to the embedder the need to make a
> policy decision, otherwise wasm serialization/deserialization won't
> work "out of the box".
>
> BUG=v8:6079
>
> Review-Url: https://codereview.chromium.org/2748473004
> Cr-Commit-Position: refs/heads/master@{#43955}
> Committed: 99743ad460TBR=jbroman@chromium.org,bradnelson@chromium.org,mtrofin@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:6079
Review-Url: https://codereview.chromium.org/2762163002
Cr-Commit-Position: refs/heads/master@{#43981}
We want to restrict structured cloning in Chrome to:
- postMessage senders and receivers that are co-located
in the same process
- indexedDB (just https).
For context, on the Chrome side, we will achieve the postMessage part
by using a mechanism similar to transferrables: the
SerializedScriptValue will have a list of wasm modules, separate from
the serialized data stream; and this list won't be copied cross
process boundaries. The IDB part is achieved by explicitly opting in
reading/writing to the serialization stream. To block attack vectors
in IPC cases, the default for deserialization will be to expect data
in the wasm transfers list.
This change is the V8 side necessary to enabling this design. We
introduce TransferrableModule, an opaque datatype exposed to the
embedder. Internally, TransferrableModules are just serialized data,
because we don't have a better mechanism, at the moment, for
de-contextualizing/re-contextualizing wasm modules (wrt Isolate and
Context).
The chrome defaults will be implemented in the
serialization/deserialization delegates on that side. For the v8 side
of things, in the absence of a serialization delegate, the V8
serializer will write to serialization stream. In the absence of a
deserialization delegate, the deserializer won't work. This asymmetry
is intentional - it communicates to the embedder the need to make a
policy decision, otherwise wasm serialization/deserialization won't
work "out of the box".
BUG=v8:6079
Review-Url: https://codereview.chromium.org/2748473004
Cr-Commit-Position: refs/heads/master@{#43955}
This CL fixes unused lambda captures for big endian targets when Clang
is used for build V8.
TEST=
BUG=
Review-Url: https://codereview.chromium.org/2725613002
Cr-Commit-Position: refs/heads/master@{#43511}
This makes it no longer necessary to ensure that V8 and Blink have non-colliding
tags, which makes it easier for them to evolve independently, and also makes
the wire format more suitable for other V8 embedders, who would not
necessarily be surveyed before V8 introduced a new tag that might collide
with theirs.
BUG=chromium:686159
Review-Url: https://codereview.chromium.org/2709023003
Cr-Commit-Position: refs/heads/master@{#43466}
Add `ValueSerializer::SetTreatArrayBufferViewsAsHostObjects()` which
instructs the `ValueSerializer` to treat ArrayBufferView objects as
host objects.
BUG=v8:5926
Review-Url: https://codereview.chromium.org/2696133007
Cr-Commit-Position: refs/heads/master@{#43281}
The serializer won't ever write a more complex object. Not validating this
allows other things to be used as keys, and converted to string when the
property set actually occurs. It turns out this gives an opportunity to trigger
OOM by giving an object a key which is a very large sparse array (whose string
representation is very large).
This case is now rejected by the deserializer.
BUG=chromium:686511
Review-Url: https://codereview.chromium.org/2697023002
Cr-Commit-Position: refs/heads/master@{#43249}
This avoids the need to pull in the UTF-8 encoding code from the public API,
and allows it to take advantage of any supported way that i::String can be
encoded (one- or two-byte).
Backward compatibility is maintained, but this is the behavior beginning
with this version.
BUG=chromium:686159
Review-Url: https://codereview.chromium.org/2665653004
Cr-Commit-Position: refs/heads/master@{#42872}
Dealing with this case requires a wire format change. It is possible that an
element can be absent even in an array where the dense format was chosen
(because the array initially had no holes), if the elements are modified while
they are being serialized. In this case, a new tag for the "hole" is emitted.
The logic to treat undefined in dense arrays as an absent property is restricted
to versions of the wire format that this tag did not exist.
BUG=chromium:686159,chromium:665820
Review-Url: https://codereview.chromium.org/2660093002
Cr-Original-Commit-Position: refs/heads/master@{#42784}
Committed: dc85f4c833
Review-Url: https://codereview.chromium.org/2660093002
Cr-Commit-Position: refs/heads/master@{#42800}
Reason for revert:
Seems to break layout tests:
https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/13146https://github.com/v8/v8/wiki/Blink-layout-tests
Original issue's description:
> ValueSerializer: Distinguish between 'undefined' and an absent property.
>
> Dealing with this case requires a wire format change. It is possible that an
> element can be absent even in an array where the dense format was chosen
> (because the array initially had no holes), if the elements are modified while
> they are being serialized. In this case, a new tag for the "hole" is emitted.
>
> The logic to treat undefined in dense arrays as an absent property is restricted
> to versions of the wire format that this tag did not exist.
>
> BUG=chromium:686159,chromium:665820
>
> Review-Url: https://codereview.chromium.org/2660093002
> Cr-Commit-Position: refs/heads/master@{#42784}
> Committed: dc85f4c833TBR=jkummerow@chromium.org,jbroman@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:686159,chromium:665820
Review-Url: https://codereview.chromium.org/2667553003
Cr-Commit-Position: refs/heads/master@{#42788}
Dealing with this case requires a wire format change. It is possible that an
element can be absent even in an array where the dense format was chosen
(because the array initially had no holes), if the elements are modified while
they are being serialized. In this case, a new tag for the "hole" is emitted.
The logic to treat undefined in dense arrays as an absent property is restricted
to versions of the wire format that this tag did not exist.
BUG=chromium:686159,chromium:665820
Review-Url: https://codereview.chromium.org/2660093002
Cr-Commit-Position: refs/heads/master@{#42784}
memcpy is faster than UTF-8 encoding/decoding. This yields 10-20% wins on
serializing and deserializing long ASCII strings, according to
blink_perf.bindings -- and these are already in a fast path where the entire
string is known to be ASCII (but this has to be checked). The win may be
larger for strings in Latin-1 but not ASCII (though I suspect this is an
uncommon case).
A change is also made to make ValueSerializerTest.EncodeTwoByteStringUsesPadding
survive wire format version number changes.
This is the first of a series of wire format changes from the previous Blink
format. The deserializer continues to be able to read the old format, but
Chromium M56 will no longer be able to read the messages written by this, in M58.
BUG=chromium:686159
Review-Url: https://codereview.chromium.org/2658793004
Cr-Commit-Position: refs/heads/master@{#42753}
This patch adds destructor to ValueSerializerTest test fixture class
which reset unhandled scheduled exceptions thrown from the current test.
In some cases unhandled scheduled exceptions from current test (eg.
from one test from ValueSerializerTestWithWasm test case) produce that
Context::New(isolate()) from next test's constructor returns NULL.
This error is easily reproduced when unittest file (compiled for ARM or
MIPS simulator) is directly executed (not by tools/run_tests.py script),
so all tests are executed together. When the script is used, each test
from ValueSerializerTestWithWasm test case is separately executed and
unhandled exception from one test doesn't efect to another test from
the same test case.
BUG=
Review-Url: https://codereview.chromium.org/2644083002
Cr-Commit-Position: refs/heads/master@{#42547}
Clang just got more strict about unused lambda captures,
and that requires us to clean all places with this issue
across all the Chromium code base. This CL fixes all such
cases in V8.
BUG=chromium:681136
Review-Url: https://codereview.chromium.org/2646553002
Cr-Commit-Position: refs/heads/master@{#42523}
Reason for revert:
OK, the failure really does seem to be due to this patch: It triggers Clang to crash
FAILED: obj/test/unittests/unittests/function-body-decoder-unittest.obj
E:\b\build\slave\cache\cipd\goma/gomacc.exe ../../third_party/llvm-build/Release+Asserts/bin/clang-cl.exe /nologo /showIncludes /FC @obj/test/unittests/unittests/function-body-decoder-unittest.obj.rsp /c ../../test/unittests/wasm/function-body-decoder-unittest.cc /Foobj/test/unittests/unittests/function-body-decoder-unittest.obj /Fd"obj/test/unittests/unittests_cc.pdb"
Assertion failed: (NumGaps == 0 || Bias < MaxDefRange) && "large ranges should not have gaps", file E:\b\build\slave\win_upload_clang\build\src\third_party\llvm\lib\MC\MCCodeView.cpp, line 531
Wrote crash dump file "C:\Users\CHROME~2\AppData\Local\Temp\goma_temp.5068\clang-cl.exe-563144.dmp"
Let's leave it out for now.
Original issue's description:
> Reland of [wasm] Enforce that function bodies end with the \"end\" opcode. (patchset #1 id:1 of https://codereview.chromium.org/2628883006/ )
>
> Reason for revert:
> Try a reland; this might not have been the source of tree-closing.
>
> Original issue's description:
> > Revert of [wasm] Enforce that function bodies end with the \"end\" opcode. (patchset #3 id:40001 of https://codereview.chromium.org/2630553002/ )
> >
> > Reason for revert:
> > Caused tree to close by failing compilation:
> >
> > https://build.chromium.org/p/client.v8/builders/V8%20Win64%20-%20clang/builds/4451
> >
> > Original issue's description:
> > > [wasm] Enforce that function bodies end with the \"end\" opcode.
> > >
> > > R=rossberg@chromium.org
> > > BUG=chromium:575167
> > >
> > > Review-Url: https://codereview.chromium.org/2630553002
> > > Cr-Commit-Position: refs/heads/master@{#42286}
> > > Committed: fcc6e85ec6
> >
> > TBR=mtrofin@chromium.org,rossberg@chromium.org,jbroman@chromium.org,titzer@chromium.org
> > # Skipping CQ checks because original CL landed less than 1 days ago.
> > NOPRESUBMIT=true
> > NOTREECHECKS=true
> > NOTRY=true
> > BUG=chromium:575167
> >
> > Review-Url: https://codereview.chromium.org/2628883006
> > Cr-Commit-Position: refs/heads/master@{#42287}
> > Committed: 1d32a3989b
>
> TBR=mtrofin@chromium.org,rossberg@chromium.org,jbroman@chromium.org,titzer@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=chromium:575167
>
> Review-Url: https://codereview.chromium.org/2628203003
> Cr-Commit-Position: refs/heads/master@{#42296}
> Committed: e539bd8e0eTBR=mtrofin@chromium.org,rossberg@chromium.org,jbroman@chromium.org,titzer@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:575167
Review-Url: https://codereview.chromium.org/2633583002
Cr-Commit-Position: refs/heads/master@{#42298}
Reason for revert:
Try a reland; this might not have been the source of tree-closing.
Original issue's description:
> Revert of [wasm] Enforce that function bodies end with the \"end\" opcode. (patchset #3 id:40001 of https://codereview.chromium.org/2630553002/ )
>
> Reason for revert:
> Caused tree to close by failing compilation:
>
> https://build.chromium.org/p/client.v8/builders/V8%20Win64%20-%20clang/builds/4451
>
> Original issue's description:
> > [wasm] Enforce that function bodies end with the \"end\" opcode.
> >
> > R=rossberg@chromium.org
> > BUG=chromium:575167
> >
> > Review-Url: https://codereview.chromium.org/2630553002
> > Cr-Commit-Position: refs/heads/master@{#42286}
> > Committed: fcc6e85ec6
>
> TBR=mtrofin@chromium.org,rossberg@chromium.org,jbroman@chromium.org,titzer@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=chromium:575167
>
> Review-Url: https://codereview.chromium.org/2628883006
> Cr-Commit-Position: refs/heads/master@{#42287}
> Committed: 1d32a3989bTBR=mtrofin@chromium.org,rossberg@chromium.org,jbroman@chromium.org,titzer@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:575167
Review-Url: https://codereview.chromium.org/2628203003
Cr-Commit-Position: refs/heads/master@{#42296}
Downside: this adds all kinds of weird includes in the .cc files.
(See design doc linked in the bug.)
BUG=v8:5402
Review-Url: https://codereview.chromium.org/2622503002
Cr-Commit-Position: refs/heads/master@{#42140}
This behavior changed recently. SharedArrayBuffers should not be put in the
transfer list, because they are not detached, and that is the meaning of being
in the transfer list.
This is the V8 side of the change, the Blink side will come next.
Review-Url: https://codereview.chromium.org/2570433005
Cr-Commit-Position: refs/heads/master@{#41740}
Compatible with the current (unshipped) Blink implementation.
BUG=chromium:148757
Review-Url: https://codereview.chromium.org/2471923002
Cr-Commit-Position: refs/heads/master@{#40775}
While this seems like it should be true, the array buffer is not actually
neutered until the end of cloning. This is so that, if an exception is thrown
during serialization, the original array buffer is not left neutered. As a
result, Blink will not have neutered the buffer.
This fixes some DCHECK failures during layout tests.
BUG=chromium:148757
Review-Url: https://codereview.chromium.org/2466563002
Cr-Commit-Position: refs/heads/master@{#40675}
Found with libfuzzer. The length is automatically converted to int (thus
large sizes could become negative, even though they are legal "array sizes").
Besides that, the length is coerced to a SMI (which is an even tighter
constraint on 32-bit systems, where it limits the legal sizes to 2^30 - 1).
Add checks that the length of a dense array is below that threshold, and also
fail fast if a length that is provided obviously could not be the correct dense
length (because there isn't enough data left in the buffer to populate such an
array).
BUG=chromium:148757
Review-Url: https://codereview.chromium.org/2399873002
Cr-Commit-Position: refs/heads/master@{#40094}
Previously this would result in applying trying to find a size modulo zero,
which causes SIGFPE. This approach was preferred over adding a default case
to preserve the ability of the compiler to detect unhandled switch cases
(within the valid range of the enum).
BUG=chromium:148757
Review-Url: https://codereview.chromium.org/2395073003
Cr-Commit-Position: refs/heads/master@{#40088}
This exposes an interface for the embedder to provide a delegate which can
serialize or deserialize embedder-specific objects, like Blink's DOM wrappers.
BUG=chromium:148757
Review-Url: https://codereview.chromium.org/2327653002
Cr-Commit-Position: refs/heads/master@{#39422}
This yields a ~5% serialization time improvement on typical JSON-esque data.
The approach taken matches json-stringifier fairly closely.
BUG=chromium:148757
Review-Url: https://codereview.chromium.org/2311063004
Cr-Commit-Position: refs/heads/master@{#39254}
This restores the contract that all API methods that return Maybe<T> or
MaybeLocal<T> always throw an exception when they return nothing.
Since v8::ValueDeserializer::ReadHeader can now throw exceptions, it
needs a Local<Context> parameter so that it can set up execution state
(entering the context, etc.). The old method has been marked for
deprecation, but since this API is experimental I intend to remove it
as soon as I've removed the use from Blink.
value-serializer-unittest has been updated to expect an exception in
all decode failure cases.
BUG=chromium:148757,chromium:641964
Review-Url: https://codereview.chromium.org/2308053002
Cr-Commit-Position: refs/heads/master@{#39188}
The format of this is a little strange, and has to do with the previous
implementation maintaining a "stack" of objects as it works. As a result,
the format writes the array buffer before giving any hint that the reason
for doing so is to obtain a view wrapping it. Handling this without creating
an explicit on-heap stack requires checking whether the next tag is 'V'
after obtaining an array buffer.
BUG=chromium:148757
Review-Url: https://codereview.chromium.org/2287653002
Cr-Commit-Position: refs/heads/master@{#38984}
The embedder is expected to arrange for the array buffer contents to be
transferred into a v8::ArrayBuffer in the receiving context (generally by
assuming ownership of the externalized backing store).
BUG=chromium:148757
Review-Url: https://codereview.chromium.org/2275033003
Cr-Commit-Position: refs/heads/master@{#38948}
