[chromecast] Fix build with enable_mojo_media=true.

chromecast/browser/media/media_pipeline_backend_factory.h

+// Copyright 2016 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.
+
+#ifndef CHROMECAST_BROWSER_MEDIA_MEDIA_PIPELINE_BACKEND_FACTORY_H_
+#define CHROMECAST_BROWSER_MEDIA_MEDIA_PIPELINE_BACKEND_FACTORY_H_
+
+#include "base/callback.h"
+#include "chromecast/public/media/media_pipeline_backend.h"
+#include "chromecast/public/media/media_pipeline_device_params.h"
+
+namespace chromecast {
+namespace media {
+
+typedef base::Callback<scoped_ptr<MediaPipelineBackend>(
+    const MediaPipelineDeviceParams&)>
+    CreateMediaPipelineBackendCB;
+
+}  // media
+}  // chromecast
+
+#endif  // CHROMECAST_BROWSER_MEDIA_MEDIA_PIPELINE_BACKEND_FACTORY_H_