[heap] Unify MarkingDeque push and unshift operations.

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 14e52bada1d28fb2fd98409c3522ad08aeb33dc0..0d365f089b235037446707a693530c50816070dc 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -199,7 +199,7 @@ class IncrementalMarkingMarkingVisitor
       chunk->set_progress_bar(start_offset);
       if (start_offset < object_size) {
         if (Marking::IsGrey(Marking::MarkBitFrom(object))) {
-          heap->mark_compact_collector()->marking_deque()->UnshiftGrey(object);
+          heap->mark_compact_collector()->marking_deque()->Unshift(object);
         } else {
           DCHECK(Marking::IsBlack(Marking::MarkBitFrom(object)));
           heap->mark_compact_collector()->UnshiftBlack(object);