Provide more accurate results about used heap size via GetHeapStatistics.

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index 484497f087f418c5fb40f51679568d1bbf99bd13..40194e36125618b85cd50125da628b76d1edf712 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -1099,13 +1099,6 @@ void MarkCompactCollector::MarkLiveObjects() {
 }
 
 
-static int CountMarkedCallback(HeapObject* obj) {
-  MapWord map_word = obj->map_word();
-  map_word.ClearMark();
-  return obj->SizeFromMap(map_word.ToMap());
-}
-
-
 #ifdef DEBUG
 void MarkCompactCollector::UpdateLiveObjectCount(HeapObject* obj) {
   live_bytes_ += obj->Size();
@@ -1152,7 +1145,7 @@ bool MarkCompactCollector::SafeIsMap(HeapObject* object) {
 
 
 void MarkCompactCollector::ClearNonLiveTransitions() {
-  HeapObjectIterator map_iterator(Heap::map_space(), &CountMarkedCallback);
+  HeapObjectIterator map_iterator(Heap::map_space(), &SizeOfMarkedObject);
   // Iterate over the map space, setting map transitions that go from
   // a marked map to an unmarked map to null transitions.  At the same time,
   // set all the prototype fields of maps back to their original value,
@@ -2673,6 +2666,13 @@ void MarkCompactCollector::ReportDeleteIfNeeded(HeapObject* obj) {
 }
 
 
+int MarkCompactCollector::SizeOfMarkedObject(HeapObject* obj) {
+  MapWord map_word = obj->map_word();
+  map_word.ClearMark();
+  return obj->SizeFromMap(map_word.ToMap());
+}
+
+
 void MarkCompactCollector::Initialize() {
   StaticPointersToNewGenUpdatingVisitor::Initialize();
   StaticMarkingVisitor::Initialize();