Do V8 GC ASAP if system memory is pressured

base/memory/memory_pressure_listener.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // MemoryPressure provides static APIs for handling memory pressure on
 // platforms that have such signals, such as Android and ChromeOS.
 // The app will try to discard buffers that aren't deemed essential (individual
 // modules will implement their own policy).
 
 #ifndef BASE_MEMORY_MEMORY_PRESSURE_LISTENER_H_
@@ skipping 33 matching lines @@
 //    delete my_listener;
 //
 class BASE_EXPORT MemoryPressureListener {
  public:
   // A Java counterpart will be generated for this enum.
   // GENERATED_JAVA_ENUM_PACKAGE: org.chromium.base
   enum MemoryPressureLevel {
     // No problems, there is enough memory to use. This event is not sent via
     // callback, but the enum is used in other places to find out the current
     // state of the system.
-    MEMORY_PRESSURE_LEVEL_NONE = -1,
+    MEMORY_PRESSURE_LEVEL_NONE,
 
     // Modules are advised to free buffers that are cheap to re-allocate and not
     // immediately needed.
-    MEMORY_PRESSURE_LEVEL_MODERATE = 0,
+    MEMORY_PRESSURE_LEVEL_MODERATE,
 
     // At this level, modules are advised to free all possible memory.  The
     // alternative is to be killed by the system, which means all memory will
     // have to be re-created, plus the cost of a cold start.
-    MEMORY_PRESSURE_LEVEL_CRITICAL = 2,
+    MEMORY_PRESSURE_LEVEL_CRITICAL,
   };
 
-  typedef base::Callback<void(MemoryPressureLevel)> MemoryPressureCallback;
+  typedef Callback<void(MemoryPressureLevel)> MemoryPressureCallback;
+  typedef Callback<void(MemoryPressureLevel)> SyncMemoryPressureCallback;
 
   explicit MemoryPressureListener(
       const MemoryPressureCallback& memory_pressure_callback);
+  MemoryPressureListener(
+      const MemoryPressureCallback& memory_pressure_callback,
+      const SyncMemoryPressureCallback& sync_memory_pressure_callback);
+
   ~MemoryPressureListener();
 
   // Intended for use by the platform specific implementation.
   static void NotifyMemoryPressure(MemoryPressureLevel memory_pressure_level);
 
   // These methods should not be used anywhere else but in memory measurement
   // code, where they are intended to maintain stable conditions across
   // measurements.
   static bool AreNotificationsSuppressed();
   static void SetNotificationsSuppressed(bool suppressed);
   static void SimulatePressureNotification(
       MemoryPressureLevel memory_pressure_level);
 
+  void Notify(MemoryPressureLevel memory_pressure_level);
+  void SyncNotify(MemoryPressureLevel memory_pressure_level);
+
  private:
-  void Notify(MemoryPressureLevel memory_pressure_level);
-
   static void DoNotifyMemoryPressure(MemoryPressureLevel memory_pressure_level);
 
   MemoryPressureCallback callback_;
+  SyncMemoryPressureCallback sync_memory_pressure_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(MemoryPressureListener);
 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_MEMORY_PRESSURE_LISTENER_H_