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

src/heap/mark-compact.h

Index: src/heap/mark-compact.h
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index a76936fc923810350364a116abf117f78afca0b0..7ad8ef67f8766a345c4a09ebe5d0cbd30534480e 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -82,8 +82,6 @@ class ObjectMarking : public AllStatic {
   template <MarkBit::AccessMode access_mode = MarkBit::NON_ATOMIC>
   V8_INLINE static bool BlackToGrey(HeapObject* obj,
                                     const MarkingState& state) {
-    DCHECK(
-        (access_mode == MarkBit::ATOMIC || IsBlack<access_mode>(obj, state)));
     MarkBit markbit = MarkBitFrom(obj, state);
     if (!Marking::BlackToGrey<access_mode>(markbit)) return false;
     state.IncrementLiveBytes<access_mode>(-obj->Size());
@@ -93,18 +91,14 @@ class ObjectMarking : public AllStatic {
   template <MarkBit::AccessMode access_mode = MarkBit::NON_ATOMIC>
   V8_INLINE static bool WhiteToGrey(HeapObject* obj,
                                     const MarkingState& state) {
-    DCHECK(
-        (access_mode == MarkBit::ATOMIC || IsWhite<access_mode>(obj, state)));
     return Marking::WhiteToGrey<access_mode>(MarkBitFrom(obj, state));
   }
 
   template <MarkBit::AccessMode access_mode = MarkBit::NON_ATOMIC>
   V8_INLINE static bool WhiteToBlack(HeapObject* obj,
                                      const MarkingState& state) {
-    DCHECK(
-        (access_mode == MarkBit::ATOMIC || IsWhite<access_mode>(obj, state)));
-    if (!ObjectMarking::WhiteToGrey<access_mode>(obj, state)) return false;
-    return ObjectMarking::GreyToBlack<access_mode>(obj, state);
+    return ObjectMarking::WhiteToGrey<access_mode>(obj, state) &&
+           ObjectMarking::GreyToBlack<access_mode>(obj, state);
   }
 
   template <MarkBit::AccessMode access_mode = MarkBit::NON_ATOMIC>