[iOS] Fix BVC's |-isTabScrolledToTopForBubblePresenter:|.

Now that the scroll proxy's contentInset is not guaranteed to be zero,
we need to check against the contentInset instead of CGPointZero.

Bug: 894617
Cq-Include-Trybots: luci.chromium.try:ios-simulator-cronet;luci.chromium.try:ios-simulator-full-configs
Change-Id: I5ba5131c969a4584879be905a92f0736a34d7f46
Reviewed-on: https://chromium-review.googlesource.com/c/1277674Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599161}

ios/chrome/browser/ui/browser_view_controller.mm

@@ -3057,8 +3057,10 @@ applicationCommandEndpoint:(id<ApplicationCommands>)applicationCommandEndpoint {
 
 - (BOOL)isTabScrolledToTopForBubblePresenter:(BubblePresenter*)bubblePresenter {
   DCHECK(bubblePresenter == self.bubblePresenter);
-  CGPoint scrollOffset =
-      self.currentWebState->GetWebViewProxy().scrollViewProxy.contentOffset;
+  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 =
@@ -3068,7 +3070,7 @@ applicationCommandEndpoint:(id<ApplicationCommands>)applicationCommandEndpoint {
     scrollOffset = [nativeController scrollOffset];
   }
 
-  return CGPointEqualToPoint(scrollOffset, CGPointZero);
+  return AreCGFloatsEqual(scrollOffset.y, -contentInset.top);
 }
 
 #pragma mark - SnapshotGeneratorDelegate methods