Link things together and enable the device selection for linux and mac.

content/renderer/media/webrtc_audio_device_impl.cc

Index: content/renderer/media/webrtc_audio_device_impl.cc
diff --git a/content/renderer/media/webrtc_audio_device_impl.cc b/content/renderer/media/webrtc_audio_device_impl.cc
index 240ea8974dc811378b494939b588ac78fb4823b8..3b589a8a023228a3cab882f6fd7c9e9a3c61d3db 100644
--- a/content/renderer/media/webrtc_audio_device_impl.cc
+++ b/content/renderer/media/webrtc_audio_device_impl.cc
@@ -6,6 +6,7 @@
 
 #include "base/bind.h"
 #include "base/string_util.h"
+#include "content/browser/renderer_host/media/audio_input_device_manager.h"
 #include "content/common/view_messages.h"
 #include "content/renderer/render_thread_impl.h"
 #include "media/audio/audio_util.h"
@@ -173,11 +174,11 @@ void WebRtcAudioDeviceImpl::Capture(
   }
 }
 
-void WebRtcAudioDeviceImpl::OnDeviceStarted(int device_index) {
-  VLOG(1) << "OnDeviceStarted (device_index=" << device_index << ")";
+void WebRtcAudioDeviceImpl::OnDeviceStarted(const std::string& device_uid) {
+  VLOG(1) << "OnDeviceStarted (device_uid=" << device_uid << ")";
   // -1 is an invalid device index. Do nothing if a valid device has
   // been started. Otherwise update the |recording_| state to false.
-  if (device_index != -1)
+  if (device_uid != media_stream::AudioInputDeviceManager::kInvalidDeviceUId)
     return;
 
   base::AutoLock auto_lock(lock_);
@@ -371,7 +372,7 @@ int32_t WebRtcAudioDeviceImpl::Init() {
     DLOG(ERROR) << "Only 48kHz sample rate is supported on Linux.";
     return -1;
   }
-  input_channels = 1;
+  input_channels = 2;
   output_channels = 1;
 
   // Based on tests using the current ALSA implementation in Chrome, we have