WIP: Eliminate event.target() usage from TrayEventFilter

ash/container_delegate.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_CONTAINER_DELEGATE_H_
+#define ASH_CONTAINER_DELEGATE_H_
+
+#include "ash/ash_export.h"
+
+namespace views {
+class Widget;
+}
+
+namespace ash {
+
+// Allows access to the window container hierarchy, which differs between
+// classic ash (where ash itself manages the hierarchy) and mus (where the
+// window manager manages the hierarchy). The default implementation is for
+// classic ash.
+class ASH_EXPORT ContainerDelegate {
+ public:
+  virtual ~ContainerDelegate() {}
+
+  virtual bool IsInMenuContainer(views::Widget* widget) = 0;
+  virtual bool IsInStatusContainer(views::Widget* widget) = 0;
+};
+
+}  // namespace ash
+
+#endif  // ASH_CONTAINER_DELEGATE_H_