Report precise number of incrementally marked bytes to gc tracer.

src/incremental-marking.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_INCREMENTAL_MARKING_H_
 #define V8_INCREMENTAL_MARKING_H_
 
 
 #include "src/execution.h"
 #include "src/mark-compact.h"
@@ skipping 184 matching lines @@
   static void SetOldSpacePageFlags(MemoryChunk* chunk,
                                    bool is_marking,
                                    bool is_compacting);
 
   static void SetNewSpacePageFlags(NewSpacePage* chunk, bool is_marking);
 
   void EnsureMarkingDequeIsCommitted();
 
   INLINE(void ProcessMarkingDeque());
 
-  INLINE(void ProcessMarkingDeque(intptr_t bytes_to_process));
+  INLINE(intptr_t ProcessMarkingDeque(intptr_t bytes_to_process));
 
   INLINE(void VisitObject(Map* map, HeapObject* obj, int size));
 
   Heap* heap_;
 
   State state_;
   bool is_compacting_;
 
   base::VirtualMemory* marking_deque_memory_;
   bool marking_deque_memory_committed_;
@@ skipping 12 matching lines @@
   int no_marking_scope_depth_;
 
   int unscanned_bytes_of_large_object_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(IncrementalMarking);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_INCREMENTAL_MARKING_H_