Enable strict-virtual-specifiers for iOS builds.

ios/web/public/web_state/web_state.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 IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_H_
 #define IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_H_
 
 #include <string>
 
 #include "base/callback_forward.h"
@@ skipping 41 matching lines @@
     // The disposition requested by the navigation source.
     WindowOpenDisposition disposition;
 
     // The transition type of navigation.
     ui::PageTransition transition;
 
     // Whether this navigation is initiated by the renderer process.
     bool is_renderer_initiated;
   };
 
-  virtual ~WebState() {}
+  ~WebState() override {}
 
   // Gets the BrowserState associated with this WebState. Can never return null.
   virtual BrowserState* GetBrowserState() const = 0;
 
   // Opens a URL with the given disposition.  The transition specifies how this
   // navigation should be recorded in the history system (for example, typed).
   virtual void OpenURL(const OpenURLParams& params) = 0;
 
   // Gets the NavigationManager associated with this WebState. Can never return
   // null.
@@ skipping 51 matching lines @@
   // TODO(droger): Move these methods to WebStateImpl once it is in ios/.
   virtual void AddObserver(WebStateObserver* observer) = 0;
   virtual void RemoveObserver(WebStateObserver* observer) = 0;
 
   WebState() {}
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_H_