WIP: Eliminate event.target() usage from TrayEventFilter

ash/mus/container_delegate_mus.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ASH_MUS_CONTAINER_DELEGATE_MUS_H_
+#define ASH_MUS_CONTAINER_DELEGATE_MUS_H_
+
+#include "ash/container_delegate.h"
+#include "base/macros.h"
+
+namespace ash {
+namespace sysui {
+
+// See ash::ContainerDelegate.
+class ContainerDelegateMus : public ash::ContainerDelegate {
+ public:
+  ContainerDelegateMus();
+  ~ContainerDelegateMus() override;
+
+  // ash::ContainerDelegate:
+  bool IsInMenuContainer(views::Widget* widget) override;
+  bool IsInStatusContainer(views::Widget* widget) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ContainerDelegateMus);
+};
+
+}  // namespace sysui
+}  // namespace ash
+
+#endif  // ASH_MUS_CONTAINER_DELEGATE_MUS_H_