Replace FOR_EACH_OBSERVER in chromeos/ with range-based for

chromeos/audio/audio_devices_pref_handler_impl.cc

Index: chromeos/audio/audio_devices_pref_handler_impl.cc
diff --git a/chromeos/audio/audio_devices_pref_handler_impl.cc b/chromeos/audio/audio_devices_pref_handler_impl.cc
index 3a25f56c7d8d9cceb79578a4d25893971d17a335..3024bfd4c520d9ca7ba89f07fe32136ecce6cff5 100644
--- a/chromeos/audio/audio_devices_pref_handler_impl.cc
+++ b/chromeos/audio/audio_devices_pref_handler_impl.cc
@@ -244,9 +244,8 @@ void AudioDevicesPrefHandlerImpl::MigrateDeviceVolumeSettings(
 }
 
 void AudioDevicesPrefHandlerImpl::NotifyAudioPolicyChange() {
-  FOR_EACH_OBSERVER(AudioPrefObserver,
-                    observers_,
-                    OnAudioPolicyPrefChanged());
+  for (auto& observer : observers_)
+    observer.OnAudioPolicyPrefChanged();
 }
 
 // static