Ensure grouped touch events have a common timestamp on Windows

Ensure grouped touch events have a common timestamp on Windows

Currently, we generate a new timestamp for each touch pointer update
received from the Windows platform. However, logically grouped
pointers really ought to share a common timestamp. Make this change.

BUG=394562
Committed: https://crrev.com/fbb9cae65597b4c26b4afbdace9fdab289051399
Cr-Commit-Position: refs/heads/master@{#332839}

[jdduke (slow), 2015-06-03 20:49:18]

jdduke@chromium.org changed reviewers:
+ tdresser@chromium.org

[jdduke (slow), 2015-06-03 20:49:19]

Tim, is this about what you had in mind?

[tdresser, 2015-06-04 13:03:46]

On 2015/06/03 20:49:19, jdduke wrote:
> Tim, is this about what you had in mind?

LGTM, thanks!

[jdduke (slow), 2015-06-04 15:31:54]

jdduke@chromium.org changed reviewers:
+ sadrul@chromium.org

[jdduke (slow), 2015-06-04 15:31:55]

+sadrul for owner review.

[sadrul, 2015-06-04 15:45:31]

lgtm

[jdduke (slow), 2015-06-04 15:45:52]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2015-06-04 15:46:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1153413004/20001

[commit-bot: I haz the power, 2015-06-04 16:20:10]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-06-04 16:20:55]

Patchset 2 (id:??) landed as
https://crrev.com/fbb9cae65597b4c26b4afbdace9fdab289051399
Cr-Commit-Position: refs/heads/master@{#332839}