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

extensions/browser/extension_web_contents_observer.h

 // Copyright 2014 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 EXTENSIONS_BROWSER_EXTENSION_WEB_CONTENTS_OBSERVER_H_
 #define EXTENSIONS_BROWSER_EXTENSION_WEB_CONTENTS_OBSERVER_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
@@ skipping 31 matching lines @@
 
   void RenderFrameCreated(content::RenderFrameHost* render_frame_host) override;
 
   // Per the documentation in WebContentsObserver, these two methods are
   // appropriate to track the set of current RenderFrameHosts.
   // NOTE: FrameDeleted() != RenderFrameDeleted().
   void FrameDeleted(content::RenderFrameHost* render_frame_host) override;
   void RenderFrameHostChanged(content::RenderFrameHost* old_host,
                               content::RenderFrameHost* new_host) override;
 
+  // Per the documentation in WebContentsObserver, these two methods are invoked
+  // when a Pepper plugin instance is attached/detached in the page DOM.
+  void PepperInstanceCreated() override;
+  void PepperInstanceDeleted() override;
+
   // Returns the extension or app associated with a render view host. Returns
   // NULL if the render view host is not for a valid extension.
   const Extension* GetExtension(content::RenderViewHost* render_view_host);
 
   // Updates ViewType for RenderViewHost based on GetViewType(web_contents()).
   void NotifyRenderViewType(content::RenderViewHost* render_view_host);
 
   // Returns the extension or app ID associated with a render view host. Returns
   // the empty string if the render view host is not for a valid extension.
   static std::string GetExtensionId(content::RenderViewHost* render_view_host);
 
  private:
   // The BrowserContext associated with the WebContents being observed.
   content::BrowserContext* browser_context_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionWebContentsObserver);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_EXTENSION_WEB_CONTENTS_OBSERVER_H_