Revert of Make a pen in eraser mode visible thru PointerEvent.buttons

Revert of Make a pen in eraser mode visible thru PointerEvent.buttons (patchset #1 id:1 of https://codereview.chromium.org/2313653004/ )

Reason for revert:
Broke the build.

Original issue's description:
> Make a pen in eraser mode visible thru PointerEvent.buttons
> 
> The PointerEvent spec can't gracefully support a hovering pen in eraser
> mode because a non-zero |buttons| field indicate an active buttons
> state. The issue is currently being discussed in github:
>   https://github.com/w3c/pointerevents/issues/134
> 
> Until the spec gets fixed, this CL exposes the eraser mode in a
> spec-compliant way by hiding the eraser mode until the pen touches the
> digitizer. Edge shows the same behavior.
> 
> This CL also adds X1, X2 & Eraser button/buttons values to
> WebPointerProperties.
> 
> BUG=642455
> 
> Review-Url: https://codereview.chromium.org/2296303002
> Cr-Commit-Position: refs/heads/master@{#416360}
> (cherry picked from commit 758b11555d5e65c63258731d4fc72b7d7edea0d7)
> 
> Committed: https://chromium.googlesource.com/chromium/src/+/956dc72f92984d993e390491c90b283beda8b89c

TBR=
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=642455

[mustaq, 2016-09-06 16:07:07]

The CQ bit was checked by mustaq@chromium.org

[mustaq, 2016-09-06 16:07:07]

Created Revert of Make a pen in eraser mode visible thru PointerEvent.buttons

[commit-bot: I haz the power, 2016-09-06 16:07:34]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-09-06 16:08:47]

Committed patchset #1 (id:1)