ios: Cleanup class/struct forward declarations

ios/web/public/url_data_source_ios.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 IOS_WEB_PUBLIC_URL_DATA_SOURCE_IOS_H_
 #define IOS_WEB_PUBLIC_URL_DATA_SOURCE_IOS_H_
 
 #include <string>
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 
 namespace base {
-class MessageLoop;
 class RefCountedMemory;
 }
 
 namespace net {
 class URLRequest;
 }
 
 namespace web {
 class BrowserState;
 
@@ skipping 65 matching lines @@
   // Called to inform the source that StartDataRequest() will be called soon.
   // Gives the source an opportunity to rewrite |path| to incorporate extra
   // information from the URLRequest prior to serving.
   virtual void WillServiceRequest(const net::URLRequest* request,
                                   std::string* path) const {}
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_PUBLIC_URL_DATA_SOURCE_IOS_H_