[heap] Fix clearing markbit in LO space

Do not DCHECK live bytes as they might be inconsistent.

BUG=
TBR=hpayer@chromium.org
NOTRY=true

Review-Url: https://codereview.chromium.org/2647573004
Cr-Commit-Position: refs/heads/master@{#42565}

src/heap/spaces.cc

@@ -3041,7 +3041,7 @@ void LargeObjectSpace::ClearMarkingStateOfLiveObjects() {
   while (current != NULL) {
     HeapObject* object = current->GetObject();
     DCHECK(ObjectMarking::IsBlack(object));
-    ObjectMarking::BlackToWhite(object);
+    ObjectMarking::ClearMarkBit(object);
     Page::FromAddress(object->address())->ResetProgressBar();
     Page::FromAddress(object->address())->ResetLiveBytes();
     current = current->next_page();