extensions: Cleanup class/struct fwd declarations

extensions/browser/extension_function.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 EXTENSIONS_BROWSER_EXTENSION_FUNCTION_H_
 #define EXTENSIONS_BROWSER_EXTENSION_FUNCTION_H_
 
 #include <stddef.h>
 
 #include <list>
@@ skipping 31 matching lines @@
 class RenderFrameHost;
 class WebContents;
 }
 
 namespace extensions {
 class ExtensionFunctionDispatcher;
 class IOThreadExtensionMessageFilter;
 class QuotaLimitHeuristic;
 }
 
-namespace IPC {
-class Sender;
-}
-
 #ifdef NDEBUG
 #define EXTENSION_FUNCTION_VALIDATE(test) \
   do {                                    \
     if (!(test)) {                        \
       this->set_bad_message(true);        \
       return ValidationFailure(this);     \
     }                                     \
   } while (0)
 #else   // NDEBUG
 #define EXTENSION_FUNCTION_VALIDATE(test) CHECK(test)
@@ skipping 611 matching lines @@
  private:
   // If you're hitting a compile error here due to "final" - great! You're
   // doing the right thing, you just need to extend UIThreadExtensionFunction
   // instead of AsyncExtensionFunction.
   ResponseAction Run() final;
 
   DISALLOW_COPY_AND_ASSIGN(AsyncExtensionFunction);
 };
 
 #endif  // EXTENSIONS_BROWSER_EXTENSION_FUNCTION_H_