Do 2 GCs on LowMemoryNotification instead of 7.

src/heap.h

Index: src/heap.h
===================================================================
--- src/heap.h	(revision 12520)
+++ src/heap.h	(working copy)
@@ -1315,6 +1315,9 @@
     return disallow_allocation_failure_;
   }
 
+  bool flush_eagerly() { return flush_eagerly_; }
+  void set_flush_eagerly(bool to) { flush_eagerly_ = to; }
+
   void TracePathToObjectFrom(Object* target, Object* root);
   void TracePathToObject(Object* target);
   void TracePathToGlobal();
@@ -1772,6 +1775,9 @@
   // rates caused by the mutator allocating a lot of long-lived objects.
   bool new_space_high_promotion_mode_active_;
 
+  // For emergency memory-freeing GCs.
+  bool flush_eagerly_;
+
   // Limit that triggers a global GC on the next (normally caused) GC.  This
   // is checked when we have already decided to do a GC to help determine
   // which collector to invoke.
@@ -2196,6 +2202,16 @@
 };
 
 
+class FlushEagerly {
+ public:
+  inline FlushEagerly();
+  inline ~FlushEagerly();
+
+ private:
+  bool old_state_;
+};
+
+
 class AlwaysAllocateScope {
  public:
   inline AlwaysAllocateScope();