MapWrapper was needed on some platforms where STL wasn't supported, we now use std::map<> directly. BUG=2164 TEST=trybots R=henrike@webrtc.org, phoglund@webrtc.org, stefan@webrtc.org, wu@webrtc.org Review URL: https://webrtc-codereview.appspot.com/2001004 git-svn-id: http://webrtc.googlecode.com/svn/trunk@4530 4adac7df-926f-26a2-2b94-8c16560cd09d