Do V8 GC ASAP if system memory is pressured[reland]

content/renderer/render_thread_impl.h

 // Copyright (c) 2012 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.
 
 #ifndef CONTENT_RENDERER_RENDER_THREAD_IMPL_H_
 #define CONTENT_RENDERER_RENDER_THREAD_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 497 matching lines @@
                              const std::string& highlight_color);
 #endif
   void OnCreateNewSharedWorker(
       const WorkerProcessMsg_CreateWorker_Params& params);
   bool RendererIsHidden() const;
   void OnRendererHidden();
   void OnRendererVisible();
 
   void ReleaseFreeMemory();
 
+  void OnSyncMemoryPressure(
+      base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level);
+
   // These objects live solely on the render thread.
   std::unique_ptr<AppCacheDispatcher> appcache_dispatcher_;
   std::unique_ptr<DomStorageDispatcher> dom_storage_dispatcher_;
   std::unique_ptr<IndexedDBDispatcher> main_thread_indexed_db_dispatcher_;
   std::unique_ptr<scheduler::RendererScheduler> renderer_scheduler_;
   std::unique_ptr<RendererBlinkPlatformImpl> blink_platform_impl_;
   std::unique_ptr<ResourceDispatchThrottler> resource_dispatch_throttler_;
   std::unique_ptr<CacheStorageDispatcher> main_thread_cache_storage_dispatcher_;
   std::unique_ptr<EmbeddedWorkerDispatcher> embedded_worker_dispatcher_;
 
@@ skipping 174 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(RenderThreadImpl);
 };
 
 #if defined(COMPILER_MSVC)
 #pragma warning(pop)
 #endif
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDER_THREAD_IMPL_H_