Keep event page alive when there's some Pepper plugin on it.

content/public/browser/web_contents_observer.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_PUBLIC_BROWSER_WEB_CONTENTS_OBSERVER_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_OBSERVER_H_
 
 #include "base/process/kill.h"
 #include "base/process/process_handle.h"
 #include "content/common/content_export.h"
@@ skipping 260 matching lines @@
                                 const std::string& name) {}
 
   // This methods is invoked when the title of the WebContents is set. If the
   // title was explicitly set, |explicit_set| is true, otherwise the title was
   // synthesized and |explicit_set| is false.
   virtual void TitleWasSet(NavigationEntry* entry, bool explicit_set) {}
 
   virtual void AppCacheAccessed(const GURL& manifest_url,
                                 bool blocked_by_policy) {}
 
+  // These methods are invoked when a Pepper plugin instance is created/deleted
+  // in the DOM.
+  virtual void PepperInstanceCreated() {}
+  virtual void PepperInstanceDeleted() {}
+
   // Notification that a plugin has crashed.
   // |plugin_pid| is the process ID identifying the plugin process. Note that
   // this ID is supplied by the renderer process, so should not be trusted.
   // Besides, the corresponding process has probably died at this point. The ID
   // may even have been reused by a new process.
   virtual void PluginCrashed(const base::FilePath& plugin_path,
                              base::ProcessId plugin_pid) {}
 
   // Notification that the given plugin has hung or become unhung. This
   // notification is only for Pepper plugins.
@@ skipping 95 matching lines @@
   void ResetWebContents();
 
   WebContentsImpl* web_contents_;
 
   DISALLOW_COPY_AND_ASSIGN(WebContentsObserver);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_OBSERVER_H_