Shrink the new space and uncommit marking deque on low memory notification.

src/incremental-marking.h

Index: src/incremental-marking.h
diff --git a/src/incremental-marking.h b/src/incremental-marking.h
index cd1a41142107b22e36012739ab6651f53b594f00..d8cf159d12c979cd6545613be7f5796d6a48f00b 100644
--- a/src/incremental-marking.h
+++ b/src/incremental-marking.h
@@ -197,6 +197,8 @@ class IncrementalMarking {
     }
   }
 
+  void UncommitMarkingDeque();
+
  private:
   void set_should_hurry(bool val) {
     should_hurry_ = val;
@@ -229,6 +231,7 @@ class IncrementalMarking {
   bool is_compacting_;
 
   VirtualMemory* marking_deque_memory_;
+  bool marking_deque_memory_committed_;
   MarkingDeque marking_deque_;
 
   int steps_count_;