Ensure PreloadController is deallocated.

ios/chrome/browser/ui/preload_controller.h

 // Copyright 2012 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_CHROME_BROWSER_UI_PRELOAD_CONTROLLER_H_
 #define IOS_CHROME_BROWSER_UI_PRELOAD_CONTROLLER_H_
 
 #import <UIKit/UIKit.h>
 
 #include <memory>
@@ skipping 92 matching lines @@
 // Tab.
 @property(nonatomic, readonly, assign) GURL prerenderedURL;
 // The URL of the currently prefetched content.  Empty if there is no prefetched
 // content.
 @property(nonatomic, readonly, assign) GURL prefetchedURL;
 @property(nonatomic, assign) id<PreloadControllerDelegate> delegate;
 
 // Designated initializer.
 - (instancetype)initWithBrowserState:(ios::ChromeBrowserState*)browserState;
 
+// Called when the browser state this object was initialized with is being
+// destroyed.
+- (void)browserStateDestroyed;
+
 // Returns the currently prerendered Tab, or nil if none exists.  The caller
 // must retain the returned Tab if needed.  After this method is called, the
 // PrerenderController reverts to a non-prerendering state.
 - (Tab*)releasePrerenderContents;
 
 // Returns true if the content of |url| has been prefetched.
 - (BOOL)hasPrefetchedURL:(const GURL&)url;
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_PRELOAD_CONTROLLER_H_