Ash Tray: Fix message center layout when UI is RTL.

BUG=1050966

Change-Id: I45aa288e721760fee374e97d38116dd53dec9d39
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2109455Reviewed-by: Ahmed Mehfooz <amehfooz@chromium.org>
Commit-Queue: Tim Song <tengs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751939}

ash/system/message_center/unified_message_center_bubble.cc

@@ -167,7 +167,8 @@ void UnifiedMessageCenterBubble::UpdatePosition() {
   gfx::Rect anchor_rect = tray_->shelf()->GetSystemTrayAnchorRect();
 
   gfx::Insets tray_bubble_insets = GetTrayBubbleInsets();
-  int left_offset = tray_->shelf()->alignment() == ShelfAlignment::kLeft
+  int left_offset = (tray_->shelf()->alignment() == ShelfAlignment::kLeft ||
+                     base::i18n::IsRTL())
                         ? tray_bubble_insets.left()
                         : -tray_bubble_insets.right();