Implement progress bar for large objects.

src/incremental-marking.h

Index: src/incremental-marking.h
diff --git a/src/incremental-marking.h b/src/incremental-marking.h
index 6ae0f595f661c29a863fe9a201e7616eb79316ad..77d54bed4b2332f863456d1ef8aed949cbcdbb57 100644
--- a/src/incremental-marking.h
+++ b/src/incremental-marking.h
@@ -164,19 +164,6 @@ class IncrementalMarking {
 
   inline void WhiteToGreyAndPush(HeapObject* obj, MarkBit mark_bit);
 
-  // Does white->black or keeps gray or black color. Returns true if converting
-  // white to black.
-  inline bool MarkBlackOrKeepGrey(MarkBit mark_bit) {
-    ASSERT(!Marking::IsImpossible(mark_bit));
-    if (mark_bit.Get()) {
-      // Grey or black: Keep the color.
-      return false;
-    }
-    mark_bit.Set();
-    ASSERT(Marking::IsBlack(mark_bit));
-    return true;
-  }
-
   inline int steps_count() {
     return steps_count_;
   }