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.

Review URL: https://codereview.chromium.org/153893005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248857 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248857