Install delegates for preload Tab.

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 4461 matching lines @@
     BOOL enableContextualSearch = self.active && !tab.isVoiceSearchResultsTab;
     [_contextualSearchController enableContextualSearch:enableContextualSearch];
   }
 }
 
 // Observer method, tab replaced.
 - (void)tabModel:(TabModel*)model
     didReplaceTab:(Tab*)oldTab
           withTab:(Tab*)newTab
           atIndex:(NSUInteger)index {
+  [self installDelegatesForTab:newTab];
+
   // Add |newTab|'s view to the hierarchy if it's the current Tab.
   if (self.active && model.currentTab == newTab)
     [self displayTab:newTab isNewSelection:NO];
 }
 
 // A tab has been removed, remove its views from display if necessary.
 - (void)tabModel:(TabModel*)model
     didRemoveTab:(Tab*)tab
          atIndex:(NSUInteger)index {
   // Remove stored native controllers for the tab.
@@ skipping 546 matching lines @@
 
 - (UIView*)voiceSearchButton {
   return _voiceSearchButton;
 }
 
 - (id<LogoAnimationControllerOwner>)logoAnimationControllerOwner {
   return [self currentLogoAnimationControllerOwner];
 }
 
 @end