[ios] Fix BubblePresenter logic for new NTP.

For native controllers, we don't update the contentInset, so it
doesn't make sense to compare the native contentOffset to the
CRWScrollViewProxy.contentInset.

Change-Id: I4fda19725cecbd70af2a054bd3c2132d5b0a25fd
Reviewed-on: https://chromium-review.googlesource.com/c/1333870Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607745}

ios/chrome/browser/ui/browser_view_controller.mm

@@ -3111,19 +3111,19 @@ applicationCommandEndpoint:(id<ApplicationCommands>)applicationCommandEndpoint {
 
 - (BOOL)isTabScrolledToTopForBubblePresenter:(BubblePresenter*)bubblePresenter {
   DCHECK(bubblePresenter == self.bubblePresenter);
-  CRWWebViewScrollViewProxy* scrollProxy =
-      self.currentWebState->GetWebViewProxy().scrollViewProxy;
-  CGPoint scrollOffset = scrollProxy.contentOffset;
-  UIEdgeInsets contentInset = scrollProxy.contentInset;
 
   // If there is a native controller, use the native controller's scroll offset.
   id nativeController =
       [self nativeControllerForTab:[self.tabModel currentTab]];
   if ([nativeController conformsToProtocol:@protocol(NewTabPageOwning)] &&
       [nativeController respondsToSelector:@selector(scrollOffset)]) {
-    scrollOffset = [nativeController scrollOffset];
+    return [nativeController scrollOffset].y == 0;
   }
 
+  CRWWebViewScrollViewProxy* scrollProxy =
+      self.currentWebState->GetWebViewProxy().scrollViewProxy;
+  CGPoint scrollOffset = scrollProxy.contentOffset;
+  UIEdgeInsets contentInset = scrollProxy.contentInset;
   return AreCGFloatsEqual(scrollOffset.y, -contentInset.top);
 }