Add a simple, safe gain PostProcessor.

chromecast/media/cma/backend/alsa/post_processors/governor_create.cc

+// Copyright 2017 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.
+
+#include "chromecast/media/cma/backend/alsa/post_processors/governor.h"
+#include "chromecast/public/media/audio_post_processor_shlib.h"
+
+namespace chromecast {
+namespace media {
+
+chromecast::media::AudioPostProcessor* AudioPostProcessorShlib_Create(
+    const std::string& config,
+    int channels) {
+  return static_cast<chromecast::media::AudioPostProcessor*>(
+      new chromecast::media::Governor(config, channels));
+}
+
+}  // namespace media
+}  // namespace chromecast