Move underflow threshold limits out of the video renderer.

media/base/media_switches.cc

Index: media/base/media_switches.cc
diff --git a/media/base/media_switches.cc b/media/base/media_switches.cc
index 1ae376d238459dfd2da45b93f7543432f1d227c3..ac9420126efb9f48eb247a33c2f3af1c325a0c30 100644
--- a/media/base/media_switches.cc
+++ b/media/base/media_switches.cc
@@ -110,4 +110,9 @@ const char kEnableInbandTextTracks[] = "enable-inband-text-tracks";
 const char kRequireAudioHardwareForTesting[] =
     "require-audio-hardware-for-testing";
 
+// Allows clients to override the threshold for when the media renderer will
+// declare the underflow state for the video stream when audio is present.
+// TODO(dalecurtis): Remove once experiments for http://crbug.com/470940 finish.
+const char kVideoUnderflowThresholdMs[] = "video-underflow-threshold-ms";
+
 }  // namespace switches