app_shell: Convert ExtensionsWebContentsObserver to BrowserContext from Profile

chrome/browser/extensions/extension_web_contents_observer.h

 // Copyright 2013 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_EXTENSIONS_EXTENSION_WEB_CONTENTS_OBSERVER_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_WEB_CONTENTS_OBSERVER_H_
 
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
-class Profile;
+namespace content {
+class BrowserContext;
+}
 
 namespace extensions {
 class Extension;
 struct Message;
 
 // A web contents observer that's used for WebContents in renderer and extension
-// processes.
+// processes. Grants the renderer access to certain URL patterns for extensions,
+// notifies the renderer that the extension was loaded and routes messages to
+// the MessageService.
 class ExtensionWebContentsObserver
     : public content::WebContentsObserver,
       public content::WebContentsUserData<ExtensionWebContentsObserver> {
  public:
   virtual ~ExtensionWebContentsObserver();
 
  private:
   explicit ExtensionWebContentsObserver(content::WebContents* web_contents);
   friend class content::WebContentsUserData<ExtensionWebContentsObserver>;
 
   // content::WebContentsObserver overrides.
   virtual void RenderViewCreated(
       content::RenderViewHost* render_view_host) OVERRIDE;
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
 
   void OnPostMessage(int port_id, const Message& message);
 
   // Gets the extension or app (if any) that is associated with a RVH.
   const Extension* GetExtension(content::RenderViewHost* render_view_host);
 
-  Profile* profile_;
+  // The browser context for the web contents this is observing.
+  content::BrowserContext* browser_context_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionWebContentsObserver);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_WEB_CONTENTS_OBSERVER_H_