media: Add ServiceFactory mojo interface and implementation.

media/mojo/interfaces/BUILD.gn

 # 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.
 
 import("//third_party/mojo/src/mojo/public/tools/bindings/mojom.gni")
 
 mojom("interfaces") {
   sources = [
     "content_decryption_module.mojom",
     "decryptor.mojom",
     "demuxer_stream.mojom",
     "media_renderer.mojom",
     "media_types.mojom",
+    "service_factory.mojom",
   ]
 
   if (is_chromeos) {
     sources += [ "platform_verification.mojom" ]
   }
 
   deps = [
     "//ui/mojo/geometry:interfaces",
   ]
 }