Cherry-picked Display the preload Tab if it replaces the current Tab.

ios/chrome/browser/ui/browser_view_controller.mm

Index: ios/chrome/browser/ui/browser_view_controller.mm
diff --git a/ios/chrome/browser/ui/browser_view_controller.mm b/ios/chrome/browser/ui/browser_view_controller.mm
index 6e441eae5182cd1a9199c3bc92c33da1cc362b90..2e19aae819b4c2b6f7d77518793d0ed4bb535692 100644
--- a/ios/chrome/browser/ui/browser_view_controller.mm
+++ b/ios/chrome/browser/ui/browser_view_controller.mm
@@ -4474,6 +4474,16 @@ class BrowserBookmarkModelBridge : public bookmarks::BookmarkModelObserver {
   }
 }
 
+// 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