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

ui/views/widget/widget_delegate.cc

Index: ui/views/widget/widget_delegate.cc
diff --git a/ui/views/widget/widget_delegate.cc b/ui/views/widget/widget_delegate.cc
index c98578014d63cf0704408f6e11e7da5b111e9116..a858c6300f6a132591820f263cbcc2038835e89d 100644
--- a/ui/views/widget/widget_delegate.cc
+++ b/ui/views/widget/widget_delegate.cc
@@ -142,6 +142,14 @@ bool WidgetDelegate::WillProcessWorkAreaChange() const {
   return false;
 }
 
+bool WidgetDelegate::HasHitTestMask() const {
+  return false;
+}
+
+void WidgetDelegate::GetHitTestMask(gfx::Path* mask) const {
+  DCHECK(mask);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // WidgetDelegateView: