[chromecast] Bind and run mojo media services on cma thread.

media/mojo/services/mojo_media_client.h

Index: media/mojo/services/mojo_media_client.h
diff --git a/media/mojo/services/mojo_media_client.h b/media/mojo/services/mojo_media_client.h
index ab14c507e822ce3e9f65c944ab18fcf6d4d6f700..0a1a73ce24b96b82cadd2b704e0eddab51d48f47 100644
--- a/media/mojo/services/mojo_media_client.h
+++ b/media/mojo/services/mojo_media_client.h
@@ -55,8 +55,18 @@ class MojoMediaClient {
   virtual scoped_ptr<CdmFactory> CreateCdmFactory(
       mojo::shell::mojom::InterfaceProvider* interface_provider);
 
+  // Returns the task runner to run media tasks.
+  // If it returns NULL, a default task runner will be used.
+  base::SingleThreadTaskRunner* media_task_runner() const {
+    return media_task_runner_.get();
+  }
+
  protected:
-  MojoMediaClient();
+  MojoMediaClient(
+      scoped_refptr<base::SingleThreadTaskRunner> media_task_runner);
+
+ private:
+  const scoped_refptr<base::SingleThreadTaskRunner> media_task_runner_;
 };
 
 }  // namespace media