Provide more accurate results about used heap size via GetHeapStatistics.

src/api.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3254 matching lines @@
 
 HeapStatistics::HeapStatistics(): total_heap_size_(0),
                                   total_heap_size_executable_(0),
                                   used_heap_size_(0) { }
 
 
 void v8::V8::GetHeapStatistics(HeapStatistics* heap_statistics) {
   heap_statistics->set_total_heap_size(i::Heap::CommittedMemory());
   heap_statistics->set_total_heap_size_executable(
       i::Heap::CommittedMemoryExecutable());
-  heap_statistics->set_used_heap_size(i::Heap::SizeOfObjects());
+  heap_statistics->set_used_heap_size(i::Heap::SizeOfObjectsSlow());
 }
 
 
 bool v8::V8::IdleNotification() {
   // Returning true tells the caller that it need not
   // continue to call IdleNotification.
   if (!i::V8::IsRunning()) return true;
   return i::V8::IdleNotification();
 }
 
@@ skipping 1714 matching lines @@
 
 
 char* HandleScopeImplementer::Iterate(ObjectVisitor* v, char* storage) {
   HandleScopeImplementer* thread_local =
       reinterpret_cast<HandleScopeImplementer*>(storage);
   thread_local->IterateThis(v);
   return storage + ArchiveSpacePerThread();
 }
 
 } }  // namespace v8::internal