Split cursor location from UserDisplayManager.

The code to manage shared cursor location isn't closely related to the
other functionality in UserDisplayManager. The biggest similarity is
that cursor location is on a per user basis. Move code into
CursorLocationManager to make UserDisplayManager easier to understand.

BUG=693081

Review-Url: https://codereview.chromium.org/2696963003
Cr-Commit-Position: refs/heads/master@{#451193}
11 files changed