Added method for getting default module state and protect agains a
read/write race for child_modules_.

BUG=2731
TEST=tsan
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/5919005

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5306 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed