Estimate a (close) upper bound on the size of black-marked objects on each page.

src/mark-compact-inl.h

Index: src/mark-compact-inl.h
diff --git a/src/mark-compact-inl.h b/src/mark-compact-inl.h
index 1aa30c7d64f9d31c4e2d432104807eba8315b64d..c28e6e3e29d6507fab97ff0b2ba7da2eef4cc638 100644
--- a/src/mark-compact-inl.h
+++ b/src/mark-compact-inl.h
@@ -52,6 +52,7 @@ void MarkCompactCollector::MarkObject(HeapObject* obj, MarkBit mark_bit) {
   ASSERT(Marking::MarkBitFrom(obj) == mark_bit);
   if (!mark_bit.Get()) {
     mark_bit.Set();
+    MemoryChunk::IncrementLiveBytes(obj->address(), obj->Size());
 #ifdef DEBUG
     UpdateLiveObjectCount(obj);
 #endif
@@ -61,8 +62,10 @@ void MarkCompactCollector::MarkObject(HeapObject* obj, MarkBit mark_bit) {
 
 
 void MarkCompactCollector::SetMark(HeapObject* obj, MarkBit mark_bit) {
+  ASSERT(!mark_bit.Get());
   ASSERT(Marking::MarkBitFrom(obj) == mark_bit);
   mark_bit.Set();
+  MemoryChunk::IncrementLiveBytes(obj->address(), obj->Size());
 #ifdef DEBUG
   UpdateLiveObjectCount(obj);
 #endif