Implement ui::ClipboardMus.

ui/base/clipboard/clipboard_test_template.h

Index: ui/base/clipboard/clipboard_test_template.h
diff --git a/ui/base/clipboard/clipboard_test_template.h b/ui/base/clipboard/clipboard_test_template.h
index b2deb2210824c99ede0cd03e186eb53b9881f168..6e0a9e978ffa5ed85e388beddc89bcd893c2c164 100644
--- a/ui/base/clipboard/clipboard_test_template.h
+++ b/ui/base/clipboard/clipboard_test_template.h
@@ -56,7 +56,7 @@ class ClipboardTest : public PlatformTest {
  public:
 #if defined(USE_AURA)
   ClipboardTest()
-      : event_source_(PlatformEventSource::CreateDefault()),
+      : event_source_(ClipboardTraits::GetEventSource()),
         clipboard_(ClipboardTraits::Create()) {}
 #else
   ClipboardTest() : clipboard_(ClipboardTraits::Create()) {}
@@ -64,6 +64,8 @@ class ClipboardTest : public PlatformTest {
 
   ~ClipboardTest() override { ClipboardTraits::Destroy(clipboard_); }
 
+  bool IsMusTest() { return ClipboardTraits::IsMusTest(); }
+
  protected:
   Clipboard& clipboard() { return *clipboard_; }
 
@@ -86,6 +88,7 @@ class ClipboardTest : public PlatformTest {
 // Hack for tests that need to call static methods of ClipboardTest.
 struct NullClipboardTraits {
   static Clipboard* Create() { return nullptr; }
+  static bool IsMusTest() { return false; }
   static void Destroy(Clipboard*) {}
 };
 
@@ -366,9 +369,11 @@ TYPED_TEST(ClipboardTest, URLTest) {
 
 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_ANDROID) && \
     !defined(OS_CHROMEOS)
-  ascii_text.clear();
-  this->clipboard().ReadAsciiText(CLIPBOARD_TYPE_SELECTION, &ascii_text);
-  EXPECT_EQ(UTF16ToUTF8(url), ascii_text);
+  if (!this->IsMusTest()) {

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

Why do we exclude mus here? Wouldn't we expect this to work on Linux, even with
mus?

[Elliot Glaysher, 2016/06/06 20:10:12]

Because mus is chromeos in a linux build.

When chrome mus is enabled, any build of chrome can have --mus passed in to
activate ash. And ash doesn't have a selection clipboard.

(The other option is to always write to CLIPBOARD_TYPE_SELECTION in mus which
will usually be ignored. I think this is better.)

[dcheng, 2016/06/07 05:39:00]

It feels a bit odd, but I can live with this reasoning.

+    ascii_text.clear();
+    this->clipboard().ReadAsciiText(CLIPBOARD_TYPE_SELECTION, &ascii_text);
+    EXPECT_EQ(UTF16ToUTF8(url), ascii_text);
+  }
 #endif
 }