[iOS] Disable the Discover help bubble.

The Discover help bubble hits DCHECKs on (at least) iPads, creating a
crash loop on canary. This CL disables it until a proper fix can be
made.

Bug: 1132757
Change-Id: I7e4dc0dc9cf2fbc46e600ff00581979710697652
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2434927Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811203}

ios/chrome/browser/ui/bubble/bubble_presenter.mm

@@ -163,7 +163,11 @@ const CGFloat kBubblePresentationDelay = 1;
   // The bottom toolbar and Discover feed header menu don't use the
   // isUserEngaged, so don't check if the user is engaged here.
   [self presentBottomToolbarTipBubble];
-  [self presentDiscoverFeedHeaderTipBubble];
+
+  // TODO(crbug.com/1132757): Reenable this once the DCHECKS for bubble size in
+  // [BubbleViewControllerPresenter frameForBubbleInRect:atAnchorPoint:] stop
+  // being hit.
+  // [self presentDiscoverFeedHeaderTipBubble];
 }
 
 - (void)presentLongPressBubble {