[ObjC ARC] Converts ios/web:web to ARC.

ios/web/web_state/web_controller_observer_bridge.mm

 // Copyright 2014 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.
 
 #import "ios/web/web_state/web_controller_observer_bridge.h"
 
 #include "base/logging.h"
 #import "ios/web/public/web_state/crw_web_controller_observer.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 
 WebControllerObserverBridge::WebControllerObserverBridge(
     id<CRWWebControllerObserver> web_controller_observer,
     WebState* web_state,
     CRWWebController* web_controller)
     : WebStateObserver(web_state),
       web_controller_observer_(web_controller_observer),
       web_controller_(web_controller) {
   DCHECK(web_controller_observer_);
   DCHECK(web_controller_);
 }
 
 WebControllerObserverBridge::~WebControllerObserverBridge() {
 }
 
 void WebControllerObserverBridge::PageLoaded(
     PageLoadCompletionStatus load_completion_status) {
   if (load_completion_status == PageLoadCompletionStatus::SUCCESS &&
       [web_controller_observer_ respondsToSelector:@selector(pageLoaded:)])
     [web_controller_observer_ pageLoaded:web_controller_];
 }
 
 }  // namespace web