extensions: Cleanup class/struct fwd declarations

extensions/browser/guest_view/extension_view/extension_view_guest.h

 // Copyright 2015 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_GUEST_VIEW_EXTENSION_VIEW_EXTENSION_VIEW_GUEST_H_
 #define EXTENSIONS_BROWSER_GUEST_VIEW_EXTENSION_VIEW_EXTENSION_VIEW_GUEST_H_
 
 #include "base/macros.h"
 #include "components/guest_view/browser/guest_view.h"
 #include "extensions/browser/extension_function_dispatcher.h"
 #include "url/gurl.h"
 
-namespace content {
-class BrowserContext;
-}
-
 namespace extensions {
 
 class ExtensionViewGuest
     : public guest_view::GuestView<ExtensionViewGuest> {
  public:
   static const char Type[];
   static guest_view::GuestViewBase* Create(
       content::WebContents* owner_web_contents);
 
   // Request navigating the guest to the provided |src| URL.
@@ skipping 29 matching lines @@
 
   // The extension URL, including the extension scheme and extension ID.
   GURL extension_url_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionViewGuest);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_GUEST_VIEW_EXTENSION_VIEW_EXTENSION_VIEW_GUEST_H_