Introduce the concept of media task runner.

chromecast/media/cma/base/media_task_runner.cc

Index: chromecast/media/cma/base/media_task_runner.cc
diff --git a/chromecast/common/chromecast_config_simple.cc b/chromecast/media/cma/base/media_task_runner.cc
similarity index 55%
copy from chromecast/common/chromecast_config_simple.cc
copy to chromecast/media/cma/base/media_task_runner.cc
index f62efe524b848cf05ec0bd0438c29d801298eaf6..5b5423bbdf1cebbe2d38b536edeab29c0a40ed00 100644
--- a/chromecast/common/chromecast_config_simple.cc
+++ b/chromecast/media/cma/base/media_task_runner.cc
@@ -2,11 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "chromecast/common/chromecast_config.h"
+#include "chromecast/media/cma/base/media_task_runner.h"
 
 namespace chromecast {
+namespace media {
 
-void ChromecastConfig::RegisterPlatformPrefs(PrefRegistrySimple* registry) {
+MediaTaskRunner::MediaTaskRunner() {
 }
 
+MediaTaskRunner::~MediaTaskRunner() {
+}
+
+}  // namespace media
 }  // namespace chromecast