Revert "Make MouseCursor mutable"

This reverts commit a6db8ab8bc4b569a26633b0ca3665297f1a5349b.

TBR=dcaiafa@chromium.org

Review URL: https://webrtc-codereview.appspot.com/6079004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5311 4adac7df-926f-26a2-2b94-8c16560cd09d
4 files changed