Add IPC message to open chrome://plugins from a missing plug-in placeholder.

chrome/browser/plugin_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 CHROME_BROWSER_PLUGIN_OBSERVER_H_
 #define CHROME_BROWSER_PLUGIN_OBSERVER_H_
 #pragma once
 
 #include "base/memory/weak_ptr.h"
 #include "content/public/browser/web_contents_observer.h"
@@ skipping 30 matching lines @@
   void OnBlockedOutdatedPlugin(const string16& name, const GURL& update_url);
 #if defined(ENABLE_PLUGIN_INSTALLATION)
   void OnFindMissingPlugin(int placeholder_id, const std::string& mime_type);
 
   void FoundMissingPlugin(int placeholder_id,
                           const std::string& mime_type,
                           PluginInstaller* installer);
   void DidNotFindMissingPlugin(int placeholder_id);
   void InstallMissingPlugin(PluginInstaller* installer);
 #endif
+  void OnOpenAboutPlugins();
 
   base::WeakPtrFactory<PluginObserver> weak_ptr_factory_;
 
   TabContentsWrapper* tab_contents_;
 
 #if defined(ENABLE_PLUGIN_INSTALLATION)
   ScopedVector<MissingPluginHost> missing_plugins_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(PluginObserver);
 };
 
 #endif  // CHROME_BROWSER_PLUGIN_OBSERVER_H_