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

media/mojo/interfaces/content_decryption_module_factory.mojom

+// Copyright 2014 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.
+
+module mojo;
+
+import "media/mojo/interfaces/content_decryption_module.mojom";
+
+// An interface to request a ContentDecryptionModule service for |key_system|
+// and |security_origin|. The |cdm| can be null if the requested service is not
+// supported (e.g. unsupported key system).
+// |cdm_id| is a client generated ID that will be used by other services to get
+// access to the CDM. See SetCdm() method in the MediaRenderer interface for
+// details.
+interface ContentDecryptionModuleFactory {
+  Create(string key_system,
+         string security_origin,
+         int32 cdm_id,
+         ContentDecryptionModule&? cdm);
+};