Standardize ECursor enum value names

This includes two updates to value names in the ECursor enum that
are required in preparation for this enum to be automatically
generated in future:
* Use k-prefix
* Rename Cross -> Crosshair

BUG=628043

Review-Url: https://codereview.chromium.org/2640713002
Cr-Commit-Position: refs/heads/master@{#444981}
6 files changed