Ensure that mask layer is of the same size as the owning layer.

ui/views/bubble/tray_bubble_view.cc

Index: ui/views/bubble/tray_bubble_view.cc
diff --git a/ui/views/bubble/tray_bubble_view.cc b/ui/views/bubble/tray_bubble_view.cc
index 9f106c168b7633118f05d0baad7fa7948346138d..816b701c8bb73644c37d2768f87186e75474bf6c 100644
--- a/ui/views/bubble/tray_bubble_view.cc
+++ b/ui/views/bubble/tray_bubble_view.cc
@@ -265,6 +265,11 @@ int TrayBubbleView::GetDialogButtons() const {
   return ui::DIALOG_BUTTON_NONE;
 }
 
+void TrayBubbleView::SizeToContents() {
+  BubbleDialogDelegateView::SizeToContents();
+  bubble_content_mask_->layer()->SetBounds(layer()->bounds());
+}
+
 void TrayBubbleView::OnBeforeBubbleWidgetInit(Widget::InitParams* params,
                                               Widget* bubble_widget) const {
   // Apply a WM-provided shadow (see ui/wm/core/).