Reland of [heap] Cleanup mark bit usage.

src/heap/mark-compact.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_HEAP_MARK_COMPACT_H_
 #define V8_HEAP_MARK_COMPACT_H_
 
 #include "src/base/bits.h"
 #include "src/heap/spaces.h"
 
@@ skipping 65 matching lines @@
   INLINE(static void MarkWhite(MarkBit mark_bit)) {
     mark_bit.Clear();
     mark_bit.Next().Clear();
   }
 
   INLINE(static void BlackToWhite(MarkBit markbit)) {
     DCHECK(IsBlack(markbit));
     markbit.Clear();
   }
 
-  INLINE(static void GreyToWhite(MarkBit markbit)) {
-    DCHECK(IsGrey(markbit));
-    markbit.Clear();
-    markbit.Next().Clear();
-  }
-
   INLINE(static void BlackToGrey(MarkBit markbit)) {
     DCHECK(IsBlack(markbit));
     markbit.Next().Set();
   }
 
   INLINE(static void WhiteToGrey(MarkBit markbit)) {
     DCHECK(IsWhite(markbit));
     markbit.Set();
     markbit.Next().Set();
   }
@@ skipping 767 matching lines @@
  private:
   MarkCompactCollector* collector_;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_MARK_COMPACT_H_