Add a ref counted audio bus.

media/base/audio_bus.cc

Index: media/base/audio_bus.cc
diff --git a/media/base/audio_bus.cc b/media/base/audio_bus.cc
index e34c7489399695b747fe44672cc0a6780a17371d..c6236b642b7eb6384f1edb56a57610467f9a1b20 100644
--- a/media/base/audio_bus.cc
+++ b/media/base/audio_bus.cc
@@ -340,4 +340,15 @@ void AudioBus::SwapChannels(int a, int b) {
   std::swap(channel_data_[a], channel_data_[b]);
 }
 
+scoped_refptr<AudioBusRefCounted> AudioBusRefCounted::Create(
+    int channels, int frames) {
+  return scoped_refptr<AudioBusRefCounted>(
+      new AudioBusRefCounted(channels, frames));
+}
+
+AudioBusRefCounted::AudioBusRefCounted(int channels, int frames)
+    : AudioBus(channels, frames) {}
+
+AudioBusRefCounted::~AudioBusRefCounted() {}
+
 }  // namespace media