media: Support creation and SetCdm() for mojo based CDM.

media/mojo/interfaces/media_renderer.mojom

Index: media/mojo/interfaces/media_renderer.mojom
diff --git a/media/mojo/interfaces/media_renderer.mojom b/media/mojo/interfaces/media_renderer.mojom
index 6b7e86e149b0f99c23ad80ec0719656f98bf6f43..35329dfd785873e1b95aa84d4f149e56cac6b2a8 100644
--- a/media/mojo/interfaces/media_renderer.mojom
+++ b/media/mojo/interfaces/media_renderer.mojom
@@ -28,6 +28,10 @@ interface MediaRenderer {
 
   // Sets the output volume. The default volume should be 1.
   SetVolume(float volume);
+
+  // Attaches the CDM associated with |cdm_id| to the renderer service,

[ddorwin, 2015/01/07 00:37:14]

nit: *media* renderer? (It just looks odd when reading it, though the file and
class have context. You could also say "this object."

+  // executing the callback with whether the CDM was successfully attached.
+  SetCdm(int32 cdm_id) => (bool success);
 };
 
 interface MediaRendererClient {