Add an initial revision of an audio server.

services/media/audio/platform/generic/mixer.cc

+// 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.
+
+#include "services/media/audio/platform/generic/mixer.h"
+#include "services/media/audio/platform/generic/mixers/no_op.h"
+#include "services/media/audio/platform/generic/mixers/point_sampler.h"
+
+namespace mojo {
+namespace media {
+namespace audio {
+
+Mixer::Mixer() {}
+Mixer::~Mixer() {}
+
+MixerPtr Mixer::Select(const LpcmMediaTypeDetailsPtr& src_format,
+                       const LpcmMediaTypeDetailsPtr& dst_format) {
+  // We should always have a source format.
+  if (!src_format) { return nullptr; }

[jeffbrown, 2015/11/04 23:43:34]

Seems worthy of a DCHECK.  Otherwise the caller has to deal with nullptr which
might be worse.

[johngro, 2015/11/06 02:20:26]

which he will immediately DCHECK about :)

I'll add another one here though.  This operation only happens when adding a
Track to an Output, so DCHECKs all around!

+
+  // If we don't have a destination format, just stick with no-op.  This is
+  // probably the ThrottleOutput we are picking a mixer for.
+  if (!dst_format) { return MixerPtr(new mixers::NoOp()); }
+
+  return mixers::PointSampler::Select(src_format, dst_format);
+}
+
+}  // namespace audio
+}  // namespace media
+}  // namespace mojo