Allow pass through buffer sizes on OSX.

media/audio/mac/audio_manager_mac.cc

Index: media/audio/mac/audio_manager_mac.cc
diff --git a/media/audio/mac/audio_manager_mac.cc b/media/audio/mac/audio_manager_mac.cc
index 60c8a3e7a6cbe5b4aafd98902e0b30462254a914..9908a0e330b6e3d1cd1dc73597e77c0874d88363 100644
--- a/media/audio/mac/audio_manager_mac.cc
+++ b/media/audio/mac/audio_manager_mac.cc
@@ -672,7 +672,13 @@ AudioParameters AudioManagerMac::GetPreferredOutputStreamParameters(
 
   const bool has_valid_input_params = input_params.IsValid();
   const int hardware_sample_rate = HardwareSampleRateForDevice(device);
-  const int buffer_size = ChooseBufferSize(hardware_sample_rate);
+
+  // Allow pass through buffer sizes.  If concurrent input and output streams
+  // exist, they will use the smallest buffer size amongst them.  As such, each
+  // stream must be able to FIFO requests appropriately when this happens.
+  int buffer_size = ChooseBufferSize(hardware_sample_rate);
+  if (has_valid_input_params)
+    buffer_size = std::max(input_params.frames_per_buffer(), buffer_size);
 
   int hardware_channels;
   if (!GetDeviceChannels(device, kAudioDevicePropertyScopeOutput,