[heap] Remove Marking::BlackToWhite and Marking::GreyToWhite.

BUG=chromium:694255

Review-Url: https://codereview.chromium.org/2737483002
Cr-Commit-Position: refs/heads/master@{#43609}

src/heap/incremental-marking.cc

@@ -143,11 +143,11 @@ void IncrementalMarking::TransferMark(Heap* heap, HeapObject* from,
 #endif
 
   if (Marking::IsBlack(old_mark_bit)) {
-    Marking::BlackToWhite(old_mark_bit);
+    Marking::MarkWhite(old_mark_bit);
     Marking::WhiteToBlack(new_mark_bit);
     return;
   } else if (Marking::IsGrey(old_mark_bit)) {
-    Marking::GreyToWhite(old_mark_bit);
+    Marking::MarkWhite(old_mark_bit);
     Marking::WhiteToGrey(new_mark_bit);
     heap->mark_compact_collector()->marking_deque()->Push(to);
     heap->incremental_marking()->RestartIfNotMarking();

src/heap/marking.h

@@ -303,17 +303,6 @@ class Marking : public AllStatic {
     markbit.Next().Clear();
   }
 
-  INLINE(static void BlackToWhite(MarkBit markbit)) {
-    DCHECK(IsBlack(markbit));
-    markbit.Clear();
-    markbit.Next().Clear();
-  }
-
-  INLINE(static void GreyToWhite(MarkBit markbit)) {
-    DCHECK(IsGrey(markbit));
-    markbit.Clear();
-  }
-
   INLINE(static void BlackToGrey(MarkBit markbit)) {
     DCHECK(IsBlack(markbit));
     markbit.Next().Clear();

test/unittests/heap/marking-unittest.cc

@@ -25,7 +25,7 @@ TEST(Marking, TransitionWhiteBlackWhite) {
     Marking::WhiteToBlack(mark_bit);
     CHECK(Marking::IsBlack(mark_bit));
     CHECK(!Marking::IsImpossible(mark_bit));
-    Marking::BlackToWhite(mark_bit);
+    Marking::MarkWhite(mark_bit);
     CHECK(Marking::IsWhite(mark_bit));
     CHECK(!Marking::IsImpossible(mark_bit));
   }
@@ -55,7 +55,7 @@ TEST(Marking, TransitionWhiteGreyBlackGrey) {
     CHECK(Marking::IsGrey(mark_bit));
     CHECK(Marking::IsBlackOrGrey(mark_bit));
     CHECK(!Marking::IsImpossible(mark_bit));
-    Marking::GreyToWhite(mark_bit);
+    Marking::MarkWhite(mark_bit);
     CHECK(Marking::IsWhite(mark_bit));
     CHECK(!Marking::IsImpossible(mark_bit));
   }