Fix button highlight flashing when entering fullscreen.

This change prevents unhighlighting if the anchor button has not changed. Highlighting was added to a button when a widget is anchored to that button. On entering fullscreen, a widget's anchor is reset regardless of whether it was changed. This would unhighlight then rehighlight the button but only be noticable on Mac.

Bug: 905992
Change-Id: I4989a45101c704105f5b4a572e028c851b6165b7
Reviewed-on: https://chromium-review.googlesource.com/c/1351106
Commit-Queue: Caroline Rising <corising@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611778}

ui/views/bubble/bubble_dialog_delegate_view.cc

@@ -221,7 +221,7 @@ void BubbleDialogDelegateView::SetHighlightedButton(
   bool visible = GetWidget() && GetWidget()->IsVisible();
   // If the Widget is visible, ensure the old highlight (if any) is removed
   // when the highlighted view changes.
-  if (visible)
+  if (visible && highlighted_button != highlighted_button_tracker_.view())
     UpdateHighlightedButton(false);
   highlighted_button_tracker_.SetView(highlighted_button);
   if (visible)