Break out WebAudio suspension code into new class. Add tests.

media/base/fake_audio_render_callback.cc

 // Copyright (c) 2012 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.
 
 // MSVC++ requires this to be set before any other includes to get M_PI.
 #define _USE_MATH_DEFINES
 
 #include <cmath>
 
 #include "media/base/fake_audio_render_callback.h"
 
 namespace media {
 
 FakeAudioRenderCallback::FakeAudioRenderCallback(double step)
     : half_fill_(false),
       step_(step),
       last_frames_delayed_(-1),
       last_channel_count_(-1),
       volume_(1) {
   reset();
 }
 
 FakeAudioRenderCallback::~FakeAudioRenderCallback() {}
 
 int FakeAudioRenderCallback::Render(AudioBus* audio_bus,
                                     uint32_t frames_delayed,
                                     uint32_t frames_skipped) {
+  return RenderInternal(audio_bus, frames_delayed, volume_);
+}
+
+double FakeAudioRenderCallback::ProvideInput(AudioBus* audio_bus,
+                                             uint32_t frames_delayed) {
+  // Volume should only be applied by the caller to ProvideInput, so don't bake
+  // it into the rendered audio.
+  RenderInternal(audio_bus, frames_delayed, 1.0);
+  return volume_;
+}
+
+int FakeAudioRenderCallback::RenderInternal(AudioBus* audio_bus,
+                                            uint32_t frames_delayed,
+                                            double volume) {
   DCHECK_LE(frames_delayed, static_cast<uint32_t>(INT_MAX));
   last_frames_delayed_ = static_cast<int>(frames_delayed);
-
   last_channel_count_ = audio_bus->channels();
 
   int number_of_frames = audio_bus->frames();
   if (half_fill_)
     number_of_frames /= 2;
 
   // Fill first channel with a sine wave.
   for (int i = 0; i < number_of_frames; ++i)
-    audio_bus->channel(0)[i] = sin(2 * M_PI * (x_ + step_ * i));
+    audio_bus->channel(0)[i] = sin(2 * M_PI * (x_ + step_ * i)) * volume;
   x_ += number_of_frames * step_;
 
   // Copy first channel into the rest of the channels.
-  for (int i = 1; i < audio_bus->channels(); ++i)
+  for (int i = 1; i < audio_bus->channels(); ++i) {
     memcpy(audio_bus->channel(i), audio_bus->channel(0),
            number_of_frames * sizeof(*audio_bus->channel(i)));
+  }
 
   return number_of_frames;
 }
 
-double FakeAudioRenderCallback::ProvideInput(AudioBus* audio_bus,
-                                             uint32_t frames_delayed) {
-  Render(audio_bus, frames_delayed, 0);
-  return volume_;
-}
-
 }  // namespace media