[heap] Move {hidden_string} into the root list.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/1292963006

Cr-Commit-Position: refs/heads/master@{#30272}

src/factory.h

@@ -625,10 +625,6 @@ class Factory final {
     isolate()->heap()->set_weak_stack_trace_list(*list);
   }
 
-  Handle<String> hidden_string() {
-    return Handle<String>(&isolate()->heap()->hidden_string_);
-  }
-
   // Allocates a new SharedFunctionInfo object.
   Handle<SharedFunctionInfo> NewSharedFunctionInfo(
       Handle<String> name, int number_of_literals, FunctionKind kind,

src/heap/heap.cc

@@ -96,7 +96,6 @@ Heap::Heap()
       optimize_for_memory_usage_(false),
       inline_allocation_disabled_(false),
       store_buffer_rebuilder_(store_buffer()),
-      hidden_string_(NULL),
       total_regexp_code_generated_(0),
       tracer_(this),
       high_survival_rate_period_length_(0),
@@ -3227,14 +3226,16 @@ void Heap::CreateInitialObjects() {
     roots_[constant_string_table[i].index] = *str;
   }
 
+  // The {hidden_string} is special because it is an empty string, but does not
+  // match any string (even the {empty_string}) when looked up in properties.
   // Allocate the hidden string which is used to identify the hidden properties
   // in JSObjects. The hash code has a special value so that it will not match
   // the empty string when searching for the property. It cannot be part of the
   // loop above because it needs to be allocated manually with the special
   // hash code in place. The hash code for the hidden_string is zero to ensure
   // that it will always be at the first entry in property descriptors.
-  hidden_string_ = *factory->NewOneByteInternalizedString(
-      OneByteVector("", 0), String::kEmptyStringHash);
+  set_hidden_string(*factory->NewOneByteInternalizedString(
+      OneByteVector("", 0), String::kEmptyStringHash));
 
   // Create the code_stubs dictionary. The initial size is set to avoid
   // expanding the dictionary during bootstrapping.
@@ -5255,9 +5256,6 @@ void Heap::IterateStrongRoots(ObjectVisitor* v, VisitMode mode) {
   v->VisitPointers(&roots_[0], &roots_[kStrongRootListLength]);
   v->Synchronize(VisitorSynchronization::kStrongRootList);
 
-  v->VisitPointer(bit_cast<Object**>(&hidden_string_));
-  v->Synchronize(VisitorSynchronization::kInternalizedString);
-
   isolate_->bootstrapper()->Iterate(v);
   v->Synchronize(VisitorSynchronization::kBootstrapper);
   isolate_->Iterate(v);

src/heap/heap.h

@@ -38,6 +38,7 @@ namespace internal {
   V(Oddball, true_value, TrueValue)                                            \
   V(Oddball, false_value, FalseValue)                                          \
   V(String, empty_string, empty_string)                                        \
+  V(String, hidden_string, hidden_string)                                      \
   V(Oddball, uninitialized_value, UninitializedValue)                          \
   V(Map, cell_map, CellMap)                                                    \
   V(Map, global_property_cell_map, GlobalPropertyCellMap)                      \
@@ -922,10 +923,6 @@ class Heap {
   PUBLIC_SYMBOL_LIST(SYMBOL_ACCESSOR)
 #undef SYMBOL_ACCESSOR
 
-  // The hidden_string is special because it is the empty string, but does
-  // not match the empty string.
-  String* hidden_string() { return hidden_string_; }
-
   void set_native_contexts_list(Object* object) {
     native_contexts_list_ = object;
   }
@@ -1808,10 +1805,6 @@ class Heap {
   static const ConstantStringTable constant_string_table[];
   static const StructTable struct_table[];
 
-  // The special hidden string which is an empty string, but does not match
-  // any string when looked up in properties.
-  String* hidden_string_;
-
   void AddPrivateGlobalSymbols(Handle<Object> private_intern_table);
 
   struct GCCallbackPair {

src/objects.h

@@ -10113,7 +10113,6 @@ class BreakPointInfo: public Struct {
   V(kExternalStringsTable, "external_strings_table", "(External strings)") \
   V(kStrongRootList, "strong_root_list", "(Strong roots)")                 \
   V(kSmiRootList, "smi_root_list", "(Smi roots)")                          \
-  V(kInternalizedString, "internalized_string", "(Internal string)")       \
   V(kBootstrapper, "bootstrapper", "(Bootstrapper)")                       \
   V(kTop, "top", "(Isolate)")                                              \
   V(kRelocatable, "relocatable", "(Relocatable)")                          \