app_list: Fix shadow bleeds over launcher button and steals mouse events

ui/app_list/app_list_bubble_border.h

Index: ui/app_list/app_list_bubble_border.h
diff --git a/ui/app_list/app_list_bubble_border.h b/ui/app_list/app_list_bubble_border.h
index 37dbceb8ebae368b7df963b7553559981f7f3a9f..15b77cfa1967ebba0bb0374c73cc69391073ee62 100644
--- a/ui/app_list/app_list_bubble_border.h
+++ b/ui/app_list/app_list_bubble_border.h
@@ -22,6 +22,8 @@ class AppListBubbleBorder : public views::BubbleBorder {
   bool ArrowAtTopOrBottom() const;
   bool ArrowOnLeftOrRight() const;
 
+  void GetMask(const gfx::Rect& bounds, gfx::Path* mask) const;
+
   void set_offset(const gfx::Point& offset) { offset_ = offset; }
   const gfx::Point& offset() const { return offset_; }