Fix Win64 warnings

This change fixes warnings about converting size_t to int.

BUG=webrtc:1323
TEST=trybots passing

Review URL: https://webrtc-codereview.appspot.com/1064004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@3419 4adac7df-926f-26a2-2b94-8c16560cd09d
9 files changed