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

ios/web/web_state/web_state_impl.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_WEB_STATE_WEB_STATE_IMPL_H_
 #define IOS_WEB_WEB_STATE_WEB_STATE_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 200 matching lines @@
   // Lazily creates (if necessary) and returns |request_group_id_|.
   // IMPORTANT: This should not be used for anything other than associating this
   // instance to network requests.
   // This function is only intended to be used in web/.
   // TODO(stuartmorgan): Move this method in an implementation file in web/.
   NSString* GetRequestGroupID();
 
   // WebState:
   WebStateDelegate* GetDelegate() override;
   void SetDelegate(WebStateDelegate* delegate) override;
+  bool IsWebUsageEnabled() const override;
+  void SetWebUsageEnabled(bool enabled) override;
   UIView* GetView() override;
   BrowserState* GetBrowserState() const override;
   void OpenURL(const WebState::OpenURLParams& params) override;
   NavigationManager* GetNavigationManager() override;
   CRWJSInjectionReceiver* GetJSInjectionReceiver() const override;
   void ExecuteJavaScript(const base::string16& javascript) override;
   void ExecuteJavaScript(const base::string16& javascript,
                          const JavaScriptResultCallback& callback) override;
   const std::string& GetContentLanguageHeader() const override;
   const std::string& GetContentsMimeType() const override;
@@ skipping 117 matching lines @@
   // any WeakPtrs to WebStateImpl are invalidated before its member variable's
   // destructors are executed, rendering them invalid.
   base::WeakPtrFactory<WebState> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WebStateImpl);
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_WEB_STATE_WEB_STATE_IMPL_H_