[chromecast] Fix build with enable_mojo_media=true.

chromecast/browser/media/BUILD.gn

 # Copyright 2015 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("//chromecast/chromecast.gni")
 import("//media/media_options.gni")
 
 source_set("media") {
   sources = [
     "cast_browser_cdm_factory.cc",
     "cast_browser_cdm_factory.h",
     "cast_media_client_android.cc",
     "cast_media_client_android.h",
+    "media_pipeline_backend_factory.h",
     "media_pipeline_host.cc",
     "media_pipeline_host.h",
   ]
 
   if (mojo_media_host == "browser") {
     sources += [
       "cast_mojo_media_client.cc",
       "cast_mojo_media_client.h",
       "cast_renderer.cc",
       "cast_renderer.h",
@@ skipping 21 matching lines @@
 
   if (is_android) {
     deps += [ "//components/cdm/browser" ]
   } else {
     sources += [
       "cma_message_filter_host.cc",
       "cma_message_filter_host.h",
     ]
   }
 }