Enable a ui test that plays video without audio stream...

chrome/browser/media_uitest.cc

Index: chrome/browser/media_uitest.cc
===================================================================
--- chrome/browser/media_uitest.cc	(revision 20328)
+++ chrome/browser/media_uitest.cc	(working copy)
@@ -47,6 +47,17 @@
   }
 };
 
+// <video> and <audio> only works stably on Windows.
+#if defined(OS_WIN)
+
+// TODO(hclam): The following test is disabled because it contains audio and
+// this test doesn't work with audio device.
 TEST_F(MediaTest, DISABLED_VideoBearH264) {
   PlayVideo("bear.mp4");
 }
+
+TEST_F(MediaTest, VideoBearSilentTheora) {
+  PlayVideo("bear_silent.ogv");
+}
+
+#endif