[ios] Added API to enable/disable web usage for WebState.

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 <stdint.h>
 
 #include <string>
@@ skipping 72 matching lines @@
          resized, there should be a single returned bitmap. */
       const std::vector<gfx::Size>&)>
           ImageDownloadCallback;
 
   ~WebState() override {}
 
   // Gets/Sets the delegate.
   virtual WebStateDelegate* GetDelegate() = 0;
   virtual void SetDelegate(WebStateDelegate* delegate) = 0;
 
+  // Whether or not a web view is allowed to exist in this WebState. Defaults
+  // to false; this should be enabled before attempting to access the view.
+  virtual bool IsWebUsageEnabled() const = 0;
+  virtual void SetWebUsageEnabled(bool enabled) = 0;
+
   // The view containing the contents of the current web page. If the view has
   // been purged due to low memory, this will recreate it. It is up to the
   // caller to size the view.
   virtual UIView* GetView() = 0;
 
   // 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).
@@ skipping 132 matching lines @@
 
   // Returns a WeakPtr<WebState> to the current WebState. Must remain private
   // and only call must be in WebStateWeakPtrFactory. Please consult that class
   // for more details. Remove as part of http://crbug.com/556736.
   virtual base::WeakPtr<WebState> AsWeakPtr() = 0;
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_PUBLIC_WEB_STATE_WEB_STATE_H_