content: Cleanup class/struct forward declarations

content/public/browser/browser_plugin_guest_delegate.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 CONTENT_PUBLIC_BROWSER_BROWSER_PLUGIN_GUEST_DELEGATE_H_
 #define CONTENT_PUBLIC_BROWSER_BROWSER_PLUGIN_GUEST_DELEGATE_H_
 
 #include "base/callback_forward.h"
 #include "base/process/kill.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/web_contents.h"
 
-namespace base {
-class DictionaryValue;
-}  // namespace base
-
 namespace gfx {
 class Size;
 }  // namespace gfx
 
 namespace content {
 
 class GuestHost;
 
 // Objects implement this interface to get notified about changes in the guest
 // WebContents and to provide necessary functionality.
@@ skipping 68 matching lines @@
 
   // TODO(ekaramad): A short workaround to force some types of guests to use
   // a BrowserPlugin even when we are using cross process frames for guests. It
   // should be removed after resolving https://crbug.com/642826).
   virtual bool CanUseCrossProcessFrames();
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_BROWSER_PLUGIN_GUEST_DELEGATE_H_