Persist the user's active audio device choice across chromeos session and reboots.

chromeos/dbus/cras_audio_client.cc

Index: chromeos/dbus/cras_audio_client.cc
diff --git a/chromeos/dbus/cras_audio_client.cc b/chromeos/dbus/cras_audio_client.cc
index d6c5b71a90d6d69a8db8ecc7799cbdc8dd051223..acb4bf7f0ff44ae3c73c9a1d259eece4ceb56352 100644
--- a/chromeos/dbus/cras_audio_client.cc
+++ b/chromeos/dbus/cras_audio_client.cc
@@ -186,6 +186,11 @@ class CrasAudioClientImpl : public CrasAudioClient {
                             dbus::ObjectProxy::EmptyResponseCallback());
   }
 
+  void WaitForServiceToBeAvailable(
+      const WaitForServiceToBeAvailableCallback& callback) override {
+    cras_proxy_->WaitForServiceToBeAvailable(callback);
+  }
+
  protected:
   void Init(dbus::Bus* bus) override {
     cras_proxy_ = bus->GetObjectProxy(cras::kCrasServiceName,