PeerConnection(Java): auto-WrapCurrentThread() when creating PeerConnectionFactory.

Various pieces of talk/ assume that the current Thread is ThreadManager'd
without checking this, so unconditionally wrap the caller's thread in case it
was created by Java code unbeknownst to ThreadManager.

BUG=2947
R=wu@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/9419004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6154 4adac7df-926f-26a2-2b94-8c16560cd09d