[heap] no longer perform GC to make heap iterable.

src/heap/heap.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 #include <map>
 
@@ skipping 748 matching lines @@
   // Trim the given array from the left. Note that this relocates the object
   // start and hence is only valid if there is only a single reference to it.
   FixedArrayBase* LeftTrimFixedArray(FixedArrayBase* obj, int elements_to_trim);
 
   // Trim the given array from the right.
   void RightTrimFixedArray(FixedArrayBase* obj, int elements_to_trim);
 
   // Converts the given boolean condition to JavaScript boolean value.
   inline Oddball* ToBoolean(bool condition);
 
-  // Check whether the heap is currently iterable.
-  bool IsHeapIterable();
-
   // Notify the heap that a context has been disposed.
   int NotifyContextDisposed(bool dependant_context);
 
   void set_native_contexts_list(Object* object) {
     native_contexts_list_ = object;
   }
   Object* native_contexts_list() const { return native_contexts_list_; }
 
   void set_allocation_sites_list(Object* object) {
     allocation_sites_list_ = object;
@@ skipping 1759 matching lines @@
  public:
   enum HeapObjectsFiltering { kNoFiltering, kFilterUnreachable };
 
   explicit HeapIterator(Heap* heap,
                         HeapObjectsFiltering filtering = kNoFiltering);
   ~HeapIterator();
 
   HeapObject* next();
 
  private:
-  struct MakeHeapIterableHelper {
-    explicit MakeHeapIterableHelper(Heap* heap) { heap->MakeHeapIterable(); }
-  };
-
   HeapObject* NextObject();
 
-  // The following two fields need to be declared in this order. Initialization
-  // order guarantees that we first make the heap iterable (which may involve
-  // allocations) and only then lock it down by not allowing further
-  // allocations.
-  MakeHeapIterableHelper make_heap_iterable_helper_;
   DisallowHeapAllocation no_heap_allocation_;
 
   Heap* heap_;
   HeapObjectsFiltering filtering_;
   HeapObjectsFilter* filter_;
   // Space iterator for iterating all the spaces.
   SpaceIterator* space_iterator_;
   // Object iterator for the space currently being iterated.
   std::unique_ptr<ObjectIterator> object_iterator_;
 };
@@ skipping 119 matching lines @@
   friend class LargeObjectSpace;
   friend class NewSpace;
   friend class PagedSpace;
   DISALLOW_COPY_AND_ASSIGN(AllocationObserver);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_HEAP_H_