Add BUILD.gn files for chromecast/media

chromecast/media/cma/BUILD.gn

Index: chromecast/media/cma/BUILD.gn
diff --git a/chromecast/media/cma/BUILD.gn b/chromecast/media/cma/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..c9da6296f0e5d603cd4f0775ae1cd430b2c32f73
--- /dev/null
+++ b/chromecast/media/cma/BUILD.gn
@@ -0,0 +1,14 @@
+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+group("cma") {
+  deps = [
+    "//chromecast/media/cma/backend",
+    "//chromecast/media/cma/base",
+    "//chromecast/media/cma/filters",
+    "//chromecast/media/cma/ipc",
+    "//chromecast/media/cma/ipc_streamer",
+    "//chromecast/media/cma/pipeline",
+  ]
+}