Make a pen in eraser mode visible thru PointerEvent.buttons

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

[mustaq, 2016-09-06 14:50:32]

Description was changed from

==========
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)
==========

to

==========
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/+/956dc72f92984d993e390491c90b...
==========

[mustaq, 2016-09-06 14:50:34]

Committed patchset #1 (id:1) manually as
956dc72f92984d993e390491c90b283beda8b89c.

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

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/2314093002/ by mustaq@chromium.org.

The reason for reverting is: Broke the build..