Store the id of a contributing motion event in GestureEventData
The unified GR needs to be able to construct ui::GestureEvents from
GestureEventData objects. Currently no information on
contributing touch ids is available in GestureEventData.
This information is used for figuring out which window to target
a gesture to - the gesture is targeted to the window which the
contributing touch is locked to.
BUG=332418
Review URL: https://codereview.chromium.org/
212663010
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@261808 0039d316-1c4b-4281-b951-d872f2087c98