Do V8 GC ASAP if system memory is pressured

base/memory/memory_pressure_listener.h

Index: base/memory/memory_pressure_listener.h
diff --git a/base/memory/memory_pressure_listener.h b/base/memory/memory_pressure_listener.h
index a6ce702ccb0f68df89a80b53934a884f4463926f..b5efa494db2269687aee207c1a20ade9eae28660 100644
--- a/base/memory/memory_pressure_listener.h
+++ b/base/memory/memory_pressure_listener.h
@@ -64,9 +64,14 @@ class BASE_EXPORT MemoryPressureListener {
   };
 
   typedef base::Callback<void(MemoryPressureLevel)> MemoryPressureCallback;
+  typedef base::Callback<void(bool)> SyncMemoryPressuredCallback;
 
   explicit MemoryPressureListener(
       const MemoryPressureCallback& memory_pressure_callback);
+  explicit MemoryPressureListener(
+      const MemoryPressureCallback& memory_pressure_callback,
+      const SyncMemoryPressuredCallback& sync_memory_pressured_callback);
+
   ~MemoryPressureListener();
 
   // Intended for use by the platform specific implementation.
@@ -82,11 +87,14 @@ class BASE_EXPORT MemoryPressureListener {
 
  private:
   void Notify(MemoryPressureLevel memory_pressure_level);
+  void SyncNotify(MemoryPressureLevel memory_pressure_level);
 
   static void DoNotifyMemoryPressure(MemoryPressureLevel memory_pressure_level);
 
   MemoryPressureCallback callback_;
 
+  SyncMemoryPressuredCallback sync_memory_pressured_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(MemoryPressureListener);
 };