Add WebPointerEvent, WebMouseProperties and WebPointerProperties types.

Add WebPointerEvent, WebMouseProperties and WebPointerProperties types.

This add a WebPointerEvent type. This also adds WebMouseProperties and
WebPointerProperties types as common types which are inherited by
WebMouseEvent, WebPointerEvent and WebTouchPoint. The latter change causes
WebTouchPoint field names to change.

This CL is a part of a three-sided patchset:
1. https://codereview.chromium.org/1216053014/  <-- this patch
2. https://codereview.chromium.org/1218663006/
3. https://codereview.chromium.org/1212113007/

[USE eero AT chromium.org, 2015-07-06 16:44:42]

e.hakkinen@samsung.com changed reviewers:
+ rbyers@chromium.org

[USE eero AT chromium.org, 2015-07-06 16:44:43]

PTAL.
As this is only an intermediate CL, it might be easier to look
https://codereview.chromium.org/1212113007/ first.

[USE eero AT chromium.org, 2015-07-06 16:44:49]

PTAL.
As this is only an intermediate CL, it might be easier to look
https://codereview.chromium.org/1212113007/ first.

[USE eero AT chromium.org, 2015-07-07 10:04:14]

Three-sided patch set is not needed, after all.