Plugin Power Saver: Add UI Overlay to throttled plugin using placeholder.

content/public/renderer/plugin_instance_throttler.h

 // Copyright 2015 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_PUBLIC_RENDERER_PLUGIN_INSTANCE_THROTTLER_H_
 #define CONTENT_PUBLIC_RENDERER_PLUGIN_INSTANCE_THROTTLER_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "content/common/content_export.h"
 
 class GURL;
+class SkBitmap;
 
 namespace content {
 
 class RenderFrame;
 
 // Plugin instances are "peripheral" if they are heuristically determined to be
 // not "essential" to the web page content. See comments on
 // RenderFrame::ShouldThrottleContent for details on these heuristics.
 enum PluginPowerSaverMode {
   // Plugin content is main content, and therefore never throttled.
@@ skipping 31 matching lines @@
   enum PowerSaverUnthrottleMethod {
     UNTHROTTLE_METHOD_NEVER = 0,
     UNTHROTTLE_METHOD_BY_CLICK = 1,
     UNTHROTTLE_METHOD_BY_WHITELIST = 2,
     UNTHROTTLE_METHOD_BY_AUDIO = 3,
     UNTHROTTLE_METHOD_NUM_ITEMS
   };
 
   class Observer {
    public:
-    virtual void OnThrottleStateChange() = 0;
+    // Guaranteed to be called before the throttle is engaged.
+    virtual void OnKeyframeExtracted(const SkBitmap* bitmap) {}
+    virtual void OnThrottleStateChange() {}
+    virtual void OnThrottlerDestroyed() {}
   };
 
   // Returns a nullptr if no throttler needed based on |power_saver_mode|.
   static scoped_ptr<PluginInstanceThrottler> Get(
       RenderFrame* frame,
       const GURL& plugin_url,
       PluginPowerSaverMode power_saver_mode);
 
   static void RecordUnthrottleMethodMetric(PowerSaverUnthrottleMethod method);
 
   virtual ~PluginInstanceThrottler() {}
 
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
 
   virtual bool IsThrottled() const = 0;
 
   // Marks the plugin as essential. Unthrottles the plugin if already throttled.
   virtual void MarkPluginEssential(PowerSaverUnthrottleMethod method) = 0;
 
  protected:
   PluginInstanceThrottler() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PluginInstanceThrottler);
 };
 }
 
 #endif  // CONTENT_PUBLIC_RENDERER_PLUGIN_INSTANCE_THROTTLER_H_