Add a helpful error in case web-inaccessible request.

chrome/renderer/extensions/extension_resource_request_policy.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_RENDERER_EXTENSIONS_EXTENSION_RESOURCE_REQUEST_POLICY_H_
 #define CHROME_RENDERER_EXTENSIONS_EXTENSION_RESOURCE_REQUEST_POLICY_H_
 #pragma once
 
 class ExtensionSet;
 class GURL;
 namespace WebKit {
 class WebFrame;
 }
 
 // Encapsulates the policy for when chrome-extension:// URLs can be requested.
 class ExtensionResourceRequestPolicy {
  public:
   // Returns true if the |resource_url| can be requested from |frame_url|.
   static bool CanRequestResource(const GURL& resource_url,
-                                 const WebKit::WebFrame* frame,
+                                 WebKit::WebFrame* frame,
                                  const ExtensionSet* loaded_extensions);
 
  private:
   ExtensionResourceRequestPolicy();
 };
 
 #endif  // CHROME_RENDERER_EXTENSIONS_EXTENSION_RESOURCE_REQUEST_POLICY_H_