views/mus: Connect cursor events to the mus window.

This makes views programs backed by a mus window able to change the
cursor for its bounds. mus already has partial support for per-window
cursors, this just needed to be plumbed.

BUG=548428

Review-Url: https://codereview.chromium.org/1945423002
Cr-Commit-Position: refs/heads/master@{#391660}
3 files changed