Split XboxControllerMac into its own file

XboxDataFetcher enumerates Xbox 360 and Xbox One gamepads connected over
USB. XboxController represents a connection to one Xbox gamepad through
this data fetcher. This CL moves the XboxController logic out of
XboxDataFetcher and into a separate file. The class is also renamed to
XboxControllerMac.

BUG=749295

Change-Id: If97c9f86a0e2bfa1dbf73438bc423c90450f2ba2
Reviewed-on: https://chromium-review.googlesource.com/752144
Commit-Queue: Matt Reynolds <mattreynolds@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513861}
5 files changed