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

media/mojo/interfaces/content_decryption_module.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/decryptor.mojom";
 
 // Transport layer of media::MediaKeys::Exception (see media/base/media_keys.h).
 // This is used for ContentDecryptionModule (CDM) promise rejections.
@@ skipping 10 matching lines @@
 
 // Transport layer of media::CdmPromise (see media/base/cdm_promise.h).
 // - When |success| is true, the promise is resolved and all other fields should
 //   be ignored.
 // - When |success| is false, the promise is rejected with |exception|,
 //   |system_code| and |error_message|.
 struct CdmPromiseResult {
   bool success;
   CdmException exception;
   uint32 system_code;
-  string error_message;
+  string? error_message;
 };
 
 // An interface that represents a CDM in the Encrypted Media Extensions (EME)
 // spec (https://w3c.github.io/encrypted-media/). See media/base/media_keys.h.
 [Client=ContentDecryptionModuleClient]
 interface ContentDecryptionModule {
   // See media::MediaKeys::SessionType.
   enum SessionType {
     TEMPORARY_SESSION,
     PERSISTENT_SESSION
@@ skipping 25 matching lines @@
   UpdateSession(string session_id, array<uint8> response)
       => (CdmPromiseResult result);
 
   // Closes the session specified by |session_id|.
   CloseSession(string session_id) => (CdmPromiseResult result);
 
   // Removes stored session data associated with the active session specified by
   // |session_id|.
   RemoveSession(string session_id) => (CdmPromiseResult result);
 
-  // Assigns the |cdm_id| to the CDM, and retrieves the |decryptor| associated
-  // with this CDM instance.
-  // A CDM implementation must choose to support either an explicit or implicit
-  // decryptor:
-  // - Explicit (non-null) decryptor: The client (e.g. media pipeline) will use
-  //   the |decryptor| directly to decrypt (and decode) encrypted buffers.
-  // - Implicit (null) decryptor: The client (e.g. media pipeline) will use the
-  //   |cdm_id| to locate a decryptor and associate it with the client.
-  // Note: In Chromium GetCdmContext() is a sync call. But we don't have an easy
-  // way to support sync calls on a mojo interface. Instead the client should
-  // generate a client side ID and pass it to the service.
-  GetCdmContext(int32 cdm_id, Decryptor&? decryptor);
+  // Retrieves the |decryptor| associated with this CDM instance.
+  // If the returned |decryptor| is not null, it will be used by the client
+  // (e.g. media pipeline) directly to decrypt (and decode) encrypted buffers.
+  GetDecryptor(Decryptor&? decryptor);
 };
 
 // Session callbacks. See media/base/media_keys.h for details.
 interface ContentDecryptionModuleClient {
   OnSessionMessage(string session_id, array<uint8> message,
                    string destination_url);
 
   OnSessionClosed(string session_id);
 
   OnSessionError(string session_id, CdmException exception,
                  uint32 system_code, string error_message);
 
   OnSessionKeysChange(string session_id, bool has_additional_usable_key);
 
   OnSessionExpirationUpdate(string session_id, int64 new_expiry_time_usec);
 };