Cherry-picked Display the preload Tab if it replaces the current 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 4456 matching lines @@
 - (void)tabModel:(TabModel*)model didChangeTab:(Tab*)tab {
   DCHECK(tab && ([_model indexOfTab:tab] != NSNotFound));
   if (tab == [_model currentTab]) {
     [self updateToolbar];
     // Disable contextual search when |tab| is a voice search result tab.
     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 {
+  // Add |newTab|'s view to the hierarchy if it's the current Tab.

[kkhorimoto, 2017/03/28 17:18:14]

Do we need the uninstall/install delegate calls here still?

[Eugene But (OOO till 7-30), 2017/03/28 17:30:32]

No, uninstalling/installing delegates methods do not exist on the branch.

+  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.
   [_nativeControllersForTabIDs removeObjectForKey:tab.tabId];
 
   // Ignore changes while the tab stack view is visible (or while suspended).
   // The display will be refreshed when this view becomes active again.
   if (!self.visible || !model.webUsageEnabled)
@@ skipping 541 matching lines @@
 
 - (UIView*)voiceSearchButton {
   return _voiceSearchButton;
 }
 
 - (id<LogoAnimationControllerOwner>)logoAnimationControllerOwner {
   return [self currentLogoAnimationControllerOwner];
 }
 
 @end