Change all system clock types to int64_t in bitrate_controller.

They are both compared to int64_t types inside the class, and is being called
with int64_t types. Could possibly cause bugs.

R=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/33529004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@7832 4adac7df-926f-26a2-2b94-8c16560cd09d
8 files changed