views/mus: Add a test to verify that Widget receives events correctly.

components/mus/public/cpp/tests/window_tree_client_impl_private.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 COMPONENTS_MUS_PUBLIC_CPP_TESTS_WINDOW_TREE_CLIENT_IMPL_PRIVATE_H_
 #define COMPONENTS_MUS_PUBLIC_CPP_TESTS_WINDOW_TREE_CLIENT_IMPL_PRIVATE_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
 
+namespace ui {
+class Event;
+}
+
 namespace mus {
 namespace mojom {
 class WindowTree;
 }
 
+class Window;
 class WindowTreeClientImpl;
 
 // Use to access implementation details of WindowTreeClientImpl.
 class WindowTreeClientImplPrivate {
  public:
   explicit WindowTreeClientImplPrivate(WindowTreeClientImpl* tree_client_impl);
+  explicit WindowTreeClientImplPrivate(Window* window);
   ~WindowTreeClientImplPrivate();
 
   uint32_t event_observer_id();
 
   // Calls OnEmbed() on the WindowTreeClientImpl.
   void OnEmbed(mojom::WindowTree* window_tree);
 
+  // Pretends that |event| has been received from the window server.
+  void CallOnWindowInputEvent(Window* window, const ui::Event& event);
+
  private:
   WindowTreeClientImpl* tree_client_impl_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeClientImplPrivate);
 };
 
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_PUBLIC_CPP_TESTS_WINDOW_TREE_CLIENT_IMPL_PRIVATE_H_