Implement ui::ClipboardMus.

ui/base/clipboard/clipboard_unittest.cc

Index: ui/base/clipboard/clipboard_unittest.cc
diff --git a/ui/base/clipboard/clipboard_unittest.cc b/ui/base/clipboard/clipboard_unittest.cc
index 96bf40b4ec4dd6882f910a6ff38acb92fb5a1741..a776674e29d4def50a275571d9499bc025e2087b 100644
--- a/ui/base/clipboard/clipboard_unittest.cc
+++ b/ui/base/clipboard/clipboard_unittest.cc
@@ -6,11 +6,23 @@
 
 #include "testing/gtest/include/gtest/gtest.h"
 
+#if defined(USE_AURA)
+#include "ui/events/platform/platform_event_source.h"
+#endif
+
 namespace ui {
 
 struct PlatformClipboardTraits {
+#if defined(USE_AURA)
+  static std::unique_ptr<PlatformEventSource> GetEventSource() {
+    return PlatformEventSource::CreateDefault();
+  }
+#endif
+
   static Clipboard* Create() { return Clipboard::GetForCurrentThread(); }
 
+  static bool IsMusTest() { return false; }
+
   static void Destroy(Clipboard* clipboard) {
     ASSERT_EQ(Clipboard::GetForCurrentThread(), clipboard);
     Clipboard::DestroyClipboardForCurrentThread();