Ensure PreloadController is deallocated.

ios/chrome/browser/ui/browser_view_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 "ios/chrome/browser/ui/browser_view_controller.h"
 
 #import <AssetsLibrary/AssetsLibrary.h>
 #import <MobileCoreServices/MobileCoreServices.h>
 #import <PassKit/PassKit.h>
 #import <Photos/Photos.h>
@@ skipping 1657 matching lines @@
   [self updateToolbarBackgroundAlpha:1.0];
   [_contextualSearchController close];
   _contextualSearchController.reset();
   [_contextualSearchPanel removeFromSuperview];
   [_contextualSearchMask removeFromSuperview];
   [_paymentRequestManager close];
   _paymentRequestManager.reset();
   BrowserListIOS::RemoveBrowser(self);
   [_toolbarController browserStateDestroyed];
   [_model browserStateDestroyed];
+  [_preloadController browserStateDestroyed];
+  _preloadController.reset();
   // The file remover needs the browser state, so needs to be destroyed now.
   _externalFileRemover.reset();
   _browserState = nullptr;
 }
 
 - (void)installFakeStatusBar {
   if (IsIPadIdiom()) {
     CGFloat statusBarHeight = StatusBarHeight();
     CGRect statusBarFrame =
         CGRectMake(0, 0, [[self view] frame].size.width, statusBarHeight);
@@ skipping 3449 matching lines @@
 
 - (UIView*)voiceSearchButton {
   return _voiceSearchButton;
 }
 
 - (id<LogoAnimationControllerOwner>)logoAnimationControllerOwner {
   return [self currentLogoAnimationControllerOwner];
 }
 
 @end