Makes it easier to snap or dock windows near the edges when using touch

Makes it easier to snap or dock windows near the edges when using touch. This is a followup on https://codereview.chromium.org/58973004/ to make the subsequent drags in the snapping sequence use the same touch fuzzing as the initial drag.

BUG=316645
TEST=ash_unittests --gtest_filter=*SystemGestureEventFilterTest.Drag*NearEdgeSnaps*
TEST=Manual:
     1. Snap a 500px wide browser window using touch screen.
     2. Continue drag to dock a window.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=248857

[varkha, 2014-02-04 16:09:37]

jamescook@, Could you please take a look? I have noticed that despite
https://codereview.chromium.org/58973004/ touch docking was unnecessarily
difficult for larger windows. This should make it as easy as for smaller
windows. Thanks!

[varkha, 2014-02-04 16:11:04]

jamescook@, Could you please take a look? I have noticed that despite
https://codereview.chromium.org/58973004/ touch docking was unnecessarily
difficult for larger windows. This should make it as easy as for narrower
windows. Thanks!

[James Cook, 2014-02-04 18:18:54]

lgtm

[varkha, 2014-02-04 18:29:16]

The CQ bit was checked by varkha@chromium.org

[commit-bot: I haz the power, 2014-02-04 18:37:18]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/varkha@chromium.org/153893005/1

[commit-bot: I haz the power, 2014-02-04 20:36:58]

Retried try job too often on linux_rel for step(s) base_unittests,
browser_tests, interactive_ui_tests, net_unittests, sync_integration_tests,
unit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...

[commit-bot: I haz the power, 2014-02-04 20:40:45]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/varkha@chromium.org/153893005/1

[commit-bot: I haz the power, 2014-02-04 23:11:47]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-02-04 23:11:47]

Retried try job too often on win_rel for step(s) base_unittests, browser_tests,
interactive_ui_tests, net_unittests, sync_integration_tests, unit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

[varkha, 2014-02-05 00:37:29]

The CQ bit was checked by varkha@chromium.org

[commit-bot: I haz the power, 2014-02-05 03:47:20]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/varkha@chromium.org/153893005/1

[commit-bot: I haz the power, 2014-02-05 05:19:46]

Change committed as 248857