[heap] Make non-atomic markbit operations consistent with atomic ones.

src/heap/mark-compact-inl.h

Index: src/heap/mark-compact-inl.h
diff --git a/src/heap/mark-compact-inl.h b/src/heap/mark-compact-inl.h
index cb280e2bbb0dc9a179c29d59511fddc0b5610044..584f86dc8819513643dc56dfae03751e55e747e9 100644
--- a/src/heap/mark-compact-inl.h
+++ b/src/heap/mark-compact-inl.h
@@ -38,19 +38,15 @@ void MarkCompactCollector::UnshiftBlack(HeapObject* obj) {
 }
 
 void MarkCompactCollector::MarkObject(HeapObject* obj) {
-  if (ObjectMarking::IsWhite<MarkBit::NON_ATOMIC>(
+  if (ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
           obj, MarkingState::Internal(obj))) {
-    ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
-        obj, MarkingState::Internal(obj));
     PushBlack(obj);
   }
 }
 
 void MinorMarkCompactCollector::MarkObject(HeapObject* obj) {
-  if (ObjectMarking::IsWhite<MarkBit::NON_ATOMIC>(
+  if (ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
           obj, MarkingState::External(obj))) {
-    ObjectMarking::WhiteToBlack<MarkBit::NON_ATOMIC>(
-        obj, MarkingState::External(obj));
     PushBlack(obj);
   }
 }