[heap] Simplify MarkingDeque implementation.

src/heap/incremental-marking.cc

Index: src/heap/incremental-marking.cc
diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
index db19165f0a310eb0dec219df1226b8333c17e96e..cb2ac1e75d95f2b9ab0e02a4b0495291f5bae2eb 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -198,11 +198,15 @@ class IncrementalMarkingMarkingVisitor
       } while (scan_until_end && start_offset < object_size);
       chunk->set_progress_bar(start_offset);
       if (start_offset < object_size) {
+        MarkCompactCollector* collector = heap->mark_compact_collector();
         if (Marking::IsGrey(Marking::MarkBitFrom(object))) {
-          heap->mark_compact_collector()->marking_deque()->UnshiftGrey(object);
+          collector->marking_deque()->UnshiftGrey(object);
         } else {
           DCHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
-          heap->mark_compact_collector()->marking_deque()->UnshiftBlack(object);
+          if (!collector->marking_deque()->UnshiftBlack(object)) {
+            MemoryChunk::IncrementLiveBytesFromGC(object, -object->Size());
+            Marking::BlackToGrey(object);
+          }
         }
         heap->incremental_marking()->NotifyIncompleteScanOfObject(
             object_size - (start_offset - already_scanned_offset));