Implement cursor changing on Mushrome.
This splits AshNativeCursorManager into an interface and creates two
implementations: one for classic ash (the original code), and one for
mushrome. The new mushrome implementation forwards to the mus window
manager interface instead of the individual windows due to how mus gets
cursors only from windows which have event handlers.
This leaves some features unimplemented, such as cursor sets, but
implements the core interface.
BUG=729798,734807,734809
Review-Url: https://codereview.chromium.org/2932563002
Cr-Commit-Position: refs/heads/master@{#481278}
20 files changed
