Add BUILD.gn files for chromecast/media

chromecast/media/cdm/BUILD.gn

 # 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.
 
-source_set("sudden_motion_sensor") {
+source_set("cdm") {
   sources = [
-    "sudden_motion_sensor_mac.cc",
-    "sudden_motion_sensor_mac.h",
+    "browser_cdm_cast.cc",
+    "browser_cdm_cast.h",
   ]
 
   deps = [
     "//base",
+    "//chromecast/media/base",
+    "//media",
   ]
+
+  configs += [ "//chromecast:config" ]
 }