Ensure PreloadController is deallocated.

ios/chrome/browser/ui/preload_controller.mm

 // 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.
 
 #import <UIKit/UIKit.h>
 
 #include "ios/chrome/browser/ui/preload_controller.h"
 
 #include "base/ios/device_util.h"
 #include "base/logging.h"
@@ skipping 120 matching lines @@
 
     [[NSNotificationCenter defaultCenter]
         addObserver:self
            selector:@selector(didReceiveMemoryWarning)
                name:UIApplicationDidReceiveMemoryWarningNotification
              object:nil];
   }
   return self;
 }
 
+- (void)browserStateDestroyed {
+  [self cancelPrerender];
+  connectionTypeObserverBridge_.reset();
+}
+
 - (void)dealloc {
   UMA_HISTOGRAM_COUNTS(kPrerendersPerSessionCountHistogramName,
                        successfulPrerendersPerSessionCount_);
   [[NSNotificationCenter defaultCenter] removeObserver:self];
   [self cancelPrerender];
   [super dealloc];
 }
 
 - (void)prerenderURL:(const GURL&)url
             referrer:(const web::Referrer&)referrer
@@ skipping 247 matching lines @@
   scheduledURL_ = GURL();
 }
 
 #pragma mark - TabDelegate
 
 - (void)discardPrerender {
   [self schedulePrerenderCancel];
 }
 
 @end