Implement ui::ClipboardMus.

ui/base/test/test_clipboard_unittest.cc

 // Copyright 2014 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/test/test_clipboard.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
 
+#if defined(USE_AURA)
+#include "ui/events/platform/platform_event_source.h"
+#endif
+
 namespace ui {
 
 struct TestClipboardTraits {
+#if defined(USE_AURA)
+  static std::unique_ptr<PlatformEventSource> GetEventSource() {
+    return PlatformEventSource::CreateDefault();

[dcheng, 2016/06/04 06:14:00]

This can just return nullptr, I think.

+  }
+#endif
+
   static Clipboard* Create() { return TestClipboard::CreateForCurrentThread(); }
 
+  static bool IsMusTest() { return false; }
+
   static void Destroy(Clipboard* clipboard) {
     ASSERT_EQ(Clipboard::GetForCurrentThread(), clipboard);
     Clipboard::DestroyClipboardForCurrentThread();
   }
 };
 
 typedef TestClipboardTraits TypesToTest;
 
 }  // namespace ui
 
 #include "ui/base/clipboard/clipboard_test_template.h"