Move pacer to fully use webrtc::Clock instead of webrtc::TickTime.

This required rewriting the send-side delay stats api to be callback based, as otherwise the SuspendBelowMinBitrate test started flaking much more frequently since it had lock order inversion problems.

R=pbos@webrtc.org, tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/21869005

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6664 4adac7df-926f-26a2-2b94-8c16560cd09d
Fixing memcheck leak suppressions for XMPPClient tests.

BUG=
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/16049004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6665 4adac7df-926f-26a2-2b94-8c16560cd09d