Implement ui::ClipboardMus.

ui/views/mus/clipboard_unittest.cc

-// Copyright 2014 The Chromium Authors. All rights reserved.
+// 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.
 
-#include "ui/base/clipboard/clipboard.h"
+#include "ui/views/mus/clipboard_mus.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
+#include "ui/events/platform/platform_event_source.h"
 
 namespace ui {
 
 struct PlatformClipboardTraits {
+  static std::unique_ptr<PlatformEventSource> GetEventSource() {
+    return std::unique_ptr<PlatformEventSource>();
+  }
+
   static Clipboard* Create() { return Clipboard::GetForCurrentThread(); }
 
   static void Destroy(Clipboard* clipboard) {
     ASSERT_EQ(Clipboard::GetForCurrentThread(), clipboard);
     Clipboard::DestroyClipboardForCurrentThread();
   }
 };
 
 typedef PlatformClipboardTraits TypesToTest;
 
 }  // namespace ui
 
 #include "ui/base/clipboard/clipboard_test_template.h"