Use a single ToplevelWindowEventHandler for the ash::Shell

ash/wm/panels/panel_window_event_handler.cc

Index: ash/wm/panels/panel_window_event_handler.cc
diff --git a/ash/wm/panels/panel_window_event_handler.cc b/ash/wm/panels/panel_window_event_handler.cc
index cb4946991951c5df45c5c3d6c72c2c38a3791f50..e1a41c0804c4dbea1e81bd37bd90642213fbcf10 100644
--- a/ash/wm/panels/panel_window_event_handler.cc
+++ b/ash/wm/panels/panel_window_event_handler.cc
@@ -13,8 +13,7 @@
 namespace ash {
 namespace internal {
 
-PanelWindowEventHandler::PanelWindowEventHandler(aura::Window* owner)
-    : ToplevelWindowEventHandler(owner) {
+PanelWindowEventHandler::PanelWindowEventHandler() {
 }
 
 PanelWindowEventHandler::~PanelWindowEventHandler() {
@@ -28,9 +27,9 @@ void PanelWindowEventHandler::OnMouseEvent(ui::MouseEvent* event) {
       target->delegate()->GetNonClientComponent(event->location()) ==
           HTCAPTION) {
     wm::GetWindowState(target)->Minimize();
+    event->StopPropagation();
     return;
   }
-  ToplevelWindowEventHandler::OnMouseEvent(event);
 }
 
 void PanelWindowEventHandler::OnGestureEvent(ui::GestureEvent* event) {
@@ -43,7 +42,6 @@ void PanelWindowEventHandler::OnGestureEvent(ui::GestureEvent* event) {
     event->StopPropagation();
     return;
   }
-  ToplevelWindowEventHandler::OnGestureEvent(event);
 }
 
 }  // namespace internal