[chromecast] Adds MediaSinkDefault.

chromecast/media/cma/backend/BUILD.gn

Index: chromecast/media/cma/backend/BUILD.gn
diff --git a/chromecast/media/cma/backend/BUILD.gn b/chromecast/media/cma/backend/BUILD.gn
index b0b18ab30ed265a8f1aeeca02fa172f98fd0a93d..26bcf8fe4306d477134d36fd9a4b9ab34e887348 100644
--- a/chromecast/media/cma/backend/BUILD.gn
+++ b/chromecast/media/cma/backend/BUILD.gn
@@ -54,6 +54,8 @@ source_set("default") {
     "cast_media_default.cc",
     "media_pipeline_backend_default.cc",
     "media_pipeline_backend_default.h",
+    "media_sink_default.cc",
+    "media_sink_default.h",
     "video_decoder_default.cc",
     "video_decoder_default.h",
   ]
@@ -62,6 +64,7 @@ source_set("default") {
     "//base",
     "//chromecast/base",
     "//chromecast/public/media",
+    "//media",
   ]
 }