chrome: Cleanup class/struct forward declarations

chrome/browser/ssl/security_state_tab_helper.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 CHROME_BROWSER_SSL_SECURITY_STATE_TAB_HELPER_H_
 #define CHROME_BROWSER_SSL_SECURITY_STATE_TAB_HELPER_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "components/security_state/core/security_state.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 #include "third_party/WebKit/public/platform/WebSecurityStyle.h"
 
 namespace content {
-struct SecurityStyleExplanations;
 class NavigationHandle;
 class WebContents;
 }  // namespace content
 
 // Tab helper provides the page's security status. Also logs console warnings
 // for private data on insecure pages.
 class SecurityStateTabHelper
     : public content::WebContentsObserver,
       public content::WebContentsUserData<SecurityStateTabHelper> {
  public:
@@ skipping 32 matching lines @@
   // HTTP pages that contain password or credit card fields. This is set
   // at most once per main-frame navigation (the first time that an HTTP
   // warning triggers on that navigation) and is used for UMA
   // histogramming.
   base::Time time_of_http_warning_on_current_navigation_;
 
   DISALLOW_COPY_AND_ASSIGN(SecurityStateTabHelper);
 };
 
 #endif  // CHROME_BROWSER_SSL_SECURITY_STATE_TAB_HELPER_H_