MemoryPressure: sends the signal to the renderer.

content/browser/renderer_host/render_widget_host_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_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_
 
 #include <deque>
 #include <list>
 #include <map>
 #include <queue>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/gtest_prod_util.h"
+#include "base/memory/memory_pressure_listener.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
 #include "base/process_util.h"
 #include "base/strings/string16.h"
 #include "base/time.h"
 #include "base/timer.h"
 #include "build/build_config.h"
 #include "content/browser/renderer_host/smooth_scroll_gesture_controller.h"
 #include "content/common/browser_rendering_stats.h"
@@ skipping 681 matching lines @@
 
   // Called on OnInputEventAck() to process a touch event ack message.
   // This can result in a gesture event being generated and sent back to the
   // renderer.
   void ProcessTouchAck(InputEventAckState ack_result);
 
   // Called when there is a new auto resize (using a post to avoid a stack
   // which may get in recursive loops).
   void DelayedAutoResized();
 
+  // Sends a memory pressure signal to the renderer.
+  void SendMemoryPressureSignal(
+      base::MemoryPressureListener::MemoryPressureLevel level);

[joth, 2013/06/21 21:52:13]

I think you want to do this at the RenderProcess, not RenderWidget level.
otherwise we will send N duplicate messages to each renderer for the N widgets
it hosts.

Also, conceptually do we need this to go to other sandbox child processes? Not
sure if we have common IPC code across process types, but if we do we could
share the message.


Android specific question: couldn't the renderers each listen to
ComponentCallbacks2.onTrimMemory themselves? It is quite possible (and likely)
that a render process will get put into the background kill list before the
browser is.

 
   // Our delegate, which wants to know mainly about keyboard events.
   // It will remain non-NULL until DetachDelegate() is called.
   RenderWidgetHostDelegate* delegate_;
 
   // Created during construction but initialized during Init*(). Therefore, it
   // is guaranteed never to be NULL, but its channel may be NULL if the
   // renderer crashed, so you must always check that.
   RenderProcessHost* process_;
 
@@ skipping 200 matching lines @@
   std::list<HWND> dummy_windows_for_activation_;
 #endif
 
   // List of callbacks for pending snapshot requests to the renderer.
   std::queue<base::Callback<void(bool, const SkBitmap&)> > pending_snapshots_;
 
   int64 last_input_number_;
 
   BrowserRenderingStats rendering_stats_;
 
+  base::MemoryPressureListener memory_pressure_listener_;
+
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_