Implement TOGGLE_EXPANSION action for the ARC notifications.

ui/message_center/views/custom_notification_view.cc

Index: ui/message_center/views/custom_notification_view.cc
diff --git a/ui/message_center/views/custom_notification_view.cc b/ui/message_center/views/custom_notification_view.cc
index bb6a4e43bb0510b059886a03df60c8a53752fe8a..b7891a5861160cd3032a11b42d1015b71f2389f6 100644
--- a/ui/message_center/views/custom_notification_view.cc
+++ b/ui/message_center/views/custom_notification_view.cc
@@ -156,4 +156,13 @@ void CustomNotificationView::ChildPreferredSizeChanged(View* child) {
     controller()->UpdateNotificationSize(notification_id());
 }
 
+bool CustomNotificationView::OnMousePressed(const ui::MouseEvent& event) {
+  // TODO(yhanada): This hack will be removed when HandleAccessibleAction will
+  // be used for handling click events.
+  if (contents_view_)

[yoshiki, 2017/03/27 06:04:51]

nit: please add brackets for multi-line if-block.

Or if (contents_view_ && contents_view->...()) is also good.

[yhanada, 2017/03/27 06:26:42]

Done. Thanks!

+    if (contents_view_->OnMousePressed(event))
+      return true;
+  return MessageView::OnMousePressed(event);
+}
+
 }  // namespace message_center