For some reason, on Xbox One gamepads the Guide button state is provided by a different message than the state of all other buttons and axes. We should start listening for this message and expose the button state as B16.

The Sync button is not consistently exposed across platforms and is typically not used for gameplay, so I'll change it to be unmapped.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/70747f0483faf431871d8d1f243a7181bcf9b2ba

commit 70747f0483faf431871d8d1f243a7181bcf9b2ba
Author: Matt Reynolds <mattreynolds@google.com>
Date: Fri Oct 20 19:22:37 2017

Map Guide button for Xbox One gamepads on Mac

The Standard Gamepad specifies that the Guide button, if present, should
be mapped to B16. Xbox One gamepads expose the Guide button in a different
message than the rest of the buttons and axes. This CL listens for the
guide message and updates the B16 button state accordingly. The sync
button, which was previously mapped to B16, is unmapped with this CL for
consistency with other platforms.

BUG= 773123 

Change-Id: If56a0f63da643d861d4aefc69b3c7e24e4770ba4
Reviewed-on: https://chromium-review.googlesource.com/727376
Commit-Queue: Matt Reynolds <mattreynolds@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510516}
[modify] https://crrev.com/70747f0483faf431871d8d1f243a7181bcf9b2ba/device/gamepad/xbox_data_fetcher_mac.h
[modify] https://crrev.com/70747f0483faf431871d8d1f243a7181bcf9b2ba/device/gamepad/xbox_data_fetcher_mac.mm

Adding the label 'TE-NeedsTriageFromMTV' as issue needs 'Xbox One gamepad' device to verify.

Thanks!

This was fixed with the commit in https://bugs.chromium.org/p/chromium/issues/detail?id=773123#c3