Defer Incognito Bubble Presentation.

Ensure that the Incognito Bubble presentation is deferred until after
the feature engagement tracker is initialized, just as the New Tab
Bubble is deferred.

Bug: 778395
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I33c86953665211a7cfafc8e27349892d01e43b80
Reviewed-on: https://chromium-review.googlesource.com/809848Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: Gregory Chatzinoff <gchatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521949}

ios/chrome/browser/ui/browser_view_controller.mm

@@ -1259,7 +1259,7 @@ applicationCommandEndpoint:(id<ApplicationCommands>)applicationCommandEndpoint {
 
 - (void)presentBubblesIfEligible {
   [self presentNewTabTipBubbleOnInitialized];
-  [self presentNewIncognitoTabTipBubble];
+  [self presentNewIncognitoTabTipBubbleOnInitialized];
 }
 
 #pragma mark - UIViewController methods