Add a simple, safe gain PostProcessor.

chromecast/media/cma/backend/alsa/post_processors/saturated_gain.h

Index: chromecast/media/cma/backend/alsa/post_processors/saturated_gain.h
diff --git a/chromecast/media/cma/backend/alsa/post_processors/saturated_gain.h b/chromecast/media/cma/backend/alsa/post_processors/saturated_gain.h
new file mode 100644
index 0000000000000000000000000000000000000000..51e195d67f5e390cc7ecaf870e72c920db3e9df4
--- /dev/null
+++ b/chromecast/media/cma/backend/alsa/post_processors/saturated_gain.h
@@ -0,0 +1,43 @@
+// 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.
+
+#ifndef CHROMECAST_MEDIA_CMA_BACKEND_ALSA_POST_PROCESSORS_SATURATED_GAIN_H_
+#define CHROMECAST_MEDIA_CMA_BACKEND_ALSA_POST_PROCESSORS_SATURATED_GAIN_H_
+
+#include <string>
+
+#include "base/macros.h"
+#include "chromecast/media/cma/backend/alsa/slew_volume.h"
+#include "chromecast/media/cma/backend/alsa/volume_map.h"
+#include "chromecast/public/media/audio_post_processor_shlib.h"
+
+namespace chromecast {
+namespace media {
+
+// Provides a simple gain, avoiding overflow.
+class SaturatedGain : public AudioPostProcessor {
+ public:
+  SaturatedGain(const std::string& config, int channels);
+  ~SaturatedGain() override;
+
+  // AudioPostProcessor implementation:
+  bool SetSampleRate(int sample_rate) override;
+  int ProcessFrames(float* data, int frames, float volume) override;
+  int GetRingingTimeInFrames() override;
+
+ private:
+  int channels_;
+  int sample_rate_;
+  float last_volume_;
+  VolumeMap volume_map_;
+  SlewVolume slew_volume_;
+  float gain_;
+
+  DISALLOW_COPY_AND_ASSIGN(SaturatedGain);
+};
+
+}  // namespace media
+}  // namespace chromecast
+
+#endif  // CHROMECAST_MEDIA_CMA_BACKEND_ALSA_POST_PROCESSORS_SATURATED_GAIN_H_