Do not make heap iterable eagerly.

src/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_H_
 #define V8_HEAP_H_
 
 #include <cmath>
 
 #include "src/allocation.h"
@@ skipping 746 matching lines @@
       int flags,
       const char* gc_reason = NULL,
       const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
 
   // Last hope GC, should try to squeeze as much as possible.
   void CollectAllAvailableGarbage(const char* gc_reason = NULL);
 
   // Check whether the heap is currently iterable.
   bool IsHeapIterable();
 
-  // Ensure that we have swept all spaces in such a way that we can iterate
-  // over all objects.  May cause a GC.
-  void MakeHeapIterable();
-
   // Notify the heap that a context has been disposed.
   int NotifyContextDisposed();
 
   inline void increment_scan_on_scavenge_pages() {
     scan_on_scavenge_pages_++;
     if (FLAG_gc_verbose) {
       PrintF("Scan-on-scavenge pages: %d\n", scan_on_scavenge_pages_);
     }
   }
 
@@ skipping 928 matching lines @@
 
   // Checks whether a global GC is necessary
   GarbageCollector SelectGarbageCollector(AllocationSpace space,
                                           const char** reason);
 
   // Make sure there is a filler value behind the top of the new space
   // so that the GC does not confuse some unintialized/stale memory
   // with the allocation memento of the object at the top
   void EnsureFillerObjectAtTop();
 
+  // Ensure that we have swept all spaces in such a way that we can iterate
+  // over all objects.  May cause a GC.
+  void MakeHeapIterable();
+
   // Performs garbage collection operation.
   // Returns whether there is a chance that another major GC could
   // collect more garbage.
   bool CollectGarbage(
       GarbageCollector collector,
       const char* gc_reason,
       const char* collector_reason,
       const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
 
   // Performs garbage collection
@@ skipping 444 matching lines @@
   ExternalStringTable external_string_table_;
 
   VisitorDispatchTable<ScavengingCallback> scavenging_visitors_table_;
 
   MemoryChunk* chunks_queued_for_free_;
 
   Mutex relocation_mutex_;
 
   int gc_callbacks_depth_;
 
+  friend class AlwaysAllocateScope;
   friend class Factory;
+  friend class GCCallbacksScope;
   friend class GCTracer;
-  friend class AlwaysAllocateScope;
-  friend class Page;
+  friend class HeapIterator;
   friend class Isolate;
   friend class MarkCompactCollector;
   friend class MarkCompactMarkingVisitor;
   friend class MapCompact;
 #ifdef VERIFY_HEAP
   friend class NoWeakObjectVerificationScope;
 #endif
-  friend class GCCallbacksScope;
+  friend class Page;
 
   DISALLOW_COPY_AND_ASSIGN(Heap);
 };
 
 
 class HeapStats {
  public:
   static const int kStartMarker = 0xDECADE00;
   static const int kEndMarker = 0xDECADE01;
 
@@ skipping 583 matching lines @@
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_