Base RWLockWrapper on rtc::SharedExclusiveLock.

Also moves rtc::Event and rtc::SharedExclusiveLock to rtc_base_approved.

R=tommi@webrtc.org
BUG=

Review URL: https://webrtc-codereview.appspot.com/38889004

Cr-Commit-Position: refs/heads/master@{#8260}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8260 4adac7df-926f-26a2-2b94-8c16560cd09d
14 files changed