Build-level separation of default CastService implementation.

chromecast/chromecast.gyp

Index: chromecast/chromecast.gyp
diff --git a/chromecast/chromecast.gyp b/chromecast/chromecast.gyp
index 3f9357659a2ae1021a2417a796173ae97be9046d..d991a5c1f02077869bb2ee0bf52e14d672ec66f2 100644
--- a/chromecast/chromecast.gyp
+++ b/chromecast/chromecast.gyp
@@ -47,8 +47,13 @@
             'internal/chromecast_internal.gyp:cast_service_internal',
           ],
         }, {
+          'dependencies': [
+            '../base/base.gyp:base',
+            '../content/content.gyp:content',
+          ],
           'sources': [
-            'service/cast_platform_init_stub.cc',
+            'service/cast_service_simple.cc',
+            'service/cast_service_simple.h',
           ],
         }],
       ],