Add |legacy_destination_url| back to SessionMessage for EME

ppapi/api/private/ppb_content_decryptor_private.idl

Index: ppapi/api/private/ppb_content_decryptor_private.idl
diff --git a/ppapi/api/private/ppb_content_decryptor_private.idl b/ppapi/api/private/ppb_content_decryptor_private.idl
index 49cc0b37042dd379378c3a8207546a185e2212f5..10f998aa41ba7a4be0c3a662512db49e287bbfcf 100644
--- a/ppapi/api/private/ppb_content_decryptor_private.idl
+++ b/ppapi/api/private/ppb_content_decryptor_private.idl
@@ -89,12 +89,17 @@ interface PPB_ContentDecryptor_Private {
    *
    * @param[in] message A <code>PP_Var</code> of type
    * <code>PP_VARTYPE_ARRAY_BUFFER</code> that contains the message.
+   *
+   * @param[in] legacy_destination_url A <code>PP_Var</code> of type
+   * <code>PP_VARTYPE_STRING</code> containing the destination URL for the
+   * message.
    */
   void SessionMessage(
       [in] PP_Instance instance,
       [in] PP_Var web_session_id,
       [in] PP_CdmMessageType message_type,
-      [in] PP_Var message);
+      [in] PP_Var message,
+      [in] PP_Var legacy_destination_url);
 
   /**
    * The keys for a session have changed.