Cleaned up the WebRtcAudioCapturer a bit.

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 7519de90a85bac94b98d79171c201c7bdbaea235..edb3e96ea02daad861b8eff2532869b6198d6f0a 100644
--- a/content/renderer/media/webrtc_audio_device_impl.cc
+++ b/content/renderer/media/webrtc_audio_device_impl.cc
@@ -436,14 +436,21 @@ void WebRtcAudioDeviceImpl::AddAudioCapturer(
   DVLOG(1) << "WebRtcAudioDeviceImpl::AddAudioCapturer()";
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(capturer.get());
-
-  // We only support one microphone today, which means the list can contain
-  // only one capturer with a valid device id.
-  DCHECK(capturer->device_id().empty() || !GetDefaultCapturer());
   base::AutoLock auto_lock(lock_);
+  DCHECK(std::find(capturers_.begin(), capturers_.end(), capturer) ==
+      capturers_.end());
   capturers_.push_back(capturer);
 }
 
+void WebRtcAudioDeviceImpl::RemoveAudioCapturer(
+    const scoped_refptr<WebRtcAudioCapturer>& capturer) {
+  DVLOG(1) << "WebRtcAudioDeviceImpl::AddAudioCapturer()";
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(capturer.get());
+  base::AutoLock auto_lock(lock_);
+  capturers_.remove(capturer);
+}
+
 scoped_refptr<WebRtcAudioCapturer>
 WebRtcAudioDeviceImpl::GetDefaultCapturer() const {
   base::AutoLock auto_lock(lock_);