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

src/incremental-marking.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 179 matching lines @@
       if (allocation_marking_factor_ < kFastMarking) {
         if (FLAG_trace_gc) {
           PrintF("Increasing marking speed to %d due to high promotion rate\n",
                  static_cast<int>(kFastMarking));
         }
         allocation_marking_factor_ = kFastMarking;
       }
     }
   }
 
+  void UncommitMarkingDeque();
+
  private:
   void set_should_hurry(bool val) {
     should_hurry_ = val;
   }
 
   int64_t SpaceLeftInOldSpace();
 
   void ResetStepCounters();
 
   void StartMarking();
@@ skipping 12 matching lines @@
   void EnsureMarkingDequeIsCommitted();
 
   void VisitGlobalContext(Context* ctx, ObjectVisitor* v);
 
   Heap* heap_;
 
   State state_;
   bool is_compacting_;
 
   VirtualMemory* marking_deque_memory_;
+  bool marking_deque_memory_committed_;
   MarkingDeque marking_deque_;
 
   int steps_count_;
   double steps_took_;
   double longest_step_;
   int64_t old_generation_space_available_at_start_of_incremental_;
   int64_t old_generation_space_used_at_start_of_incremental_;
   int steps_count_since_last_gc_;
   double steps_took_since_last_gc_;
   int64_t bytes_rescanned_;
   bool should_hurry_;
   int allocation_marking_factor_;
   intptr_t allocated_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(IncrementalMarking);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_INCREMENTAL_MARKING_H_