Added stub MediaSourcePlayer for developing behind the flag

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 43904123893639c8543d56306975e8245e0a9665..057418b23b81f2cea0c4b268a735b1b12dc93028 100644
--- a/media/base/media_switches.cc
+++ b/media/base/media_switches.cc
@@ -21,6 +21,10 @@ const char kIgnoreResolutionLimitsForAcceleratedVideoDecode[] =
 // Disables the infobar popup for accessing protected media identifier.
 const char kDisableInfobarForProtectedMediaIdentifier[] =
     "disable-infobar-for-protected-media-identifier";
+
+// Sets the MediaSource player that uses the separate media thread
+const char kEnableMediaThreadForMediaPlayback[] =
+    "enable-media-thread-for-media-playback";
 #endif
 
 #if defined(OS_LINUX) || defined(OS_FREEBSD) || defined(OS_SOLARIS)