chrome: Cleanup class/struct forward declarations

chrome/browser/previews/previews_infobar_tab_helper.h

 // Copyright 2016 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 CHROME_BROWSER_PREVIEWS_PREVIEWS_INFOBAR_TAB_HELPER_H_
 #define CHROME_BROWSER_PREVIEWS_PREVIEWS_INFOBAR_TAB_HELPER_H_
 
 #include "base/macros.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
-class GURL;
-
-namespace content {
-class RenderFrameHost;
-}
-
 // Tracks whether a previews infobar has been shown for a page. Handles showing
 // the infobar when the main frame response indicates a Lite Page.
 class PreviewsInfoBarTabHelper
     : public content::WebContentsObserver,
       public content::WebContentsUserData<PreviewsInfoBarTabHelper> {
  public:
   ~PreviewsInfoBarTabHelper() override;
 
   // Indicates whether the InfoBar for a preview has been shown for the page.
   bool displayed_preview_infobar() const {
@@ skipping 25 matching lines @@
   // True if the InfoBar for a preview has been shown for the page.
   bool displayed_preview_infobar_;
 
   // Whether an offline preview has been shown for this page.
   bool is_showing_offline_preview_;
 
   DISALLOW_COPY_AND_ASSIGN(PreviewsInfoBarTabHelper);
 };
 
 #endif  // CHROME_BROWSER_PREVIEWS_PREVIEWS_INFOBAR_TAB_HELPER_H_