ios: Cleanup class/struct forward declarations

ios/web/public/interstitials/web_interstitial.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 IOS_WEB_PUBLIC_INTERSTITIALS_WEB_INTERSTITIAL_H_
 #define IOS_WEB_PUBLIC_INTERSTITIALS_WEB_INTERSTITIAL_H_
 
 #include <memory>
 
 class GURL;
 
-namespace gfx {
-class Size;
-}
-
 namespace web {
 
 class HtmlWebInterstitialDelegate;
 class NativeWebInterstitialDelegate;
 class WebState;
 
 // This class is used for showing interstitial pages, pages that show some
 // informative message asking for user validation before reaching the target
 // page. (Navigating to a page served over bad HTTPS or a page containing
 // malware are typical cases where an interstitial is required.)
@@ skipping 37 matching lines @@
 
   // Delegates should call this method when the user has chosen to proceed to
   // the target URL.
   // Warning: 'this' has been deleted when this method returns.
   virtual void Proceed() = 0;
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_PUBLIC_INTERSTITIALS_WEB_INTERSTITIAL_H_