ios: Cleanup class/struct forward declarations

ios/chrome/browser/application_context.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_CHROME_BROWSER_APPLICATION_CONTEXT_H_
 #define IOS_CHROME_BROWSER_APPLICATION_CONTEXT_H_
 
 #include <string>
 
 #include "base/macros.h"
@@ skipping 31 matching lines @@
 }
 
 namespace physical_web {
 class PhysicalWebDataSource;
 }
 
 namespace rappor {
 class RapporService;
 }
 
-namespace safe_browsing {
-class SafeBrowsingService;
-}
-
 namespace variations {
 class VariationsService;
 }
 
 class ApplicationContext;
 class CRLSetFetcher;
 class IOSChromeIOThread;
 class PrefService;
 
 // Gets the global application context. Cannot return null.
@@ skipping 67 matching lines @@
 
  protected:
   // Sets the global ApplicationContext instance.
   static void SetApplicationContext(ApplicationContext* context);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ApplicationContext);
 };
 
 #endif  // IOS_CHROME_BROWSER_APPLICATION_CONTEXT_H_