LookaheadFilterInterpreter: Ability to suppress fling stop

We're considering moving how flings are stopped, so for now we add a
property to disable this class' generation of stop-fling gestures.

BUG=chromium-os:32057
TEST=tested on device

Change-Id: I6b4b48b87edff7cbc3694b9ba5a287f1c81183f8
Reviewed-on: https://gerrit.chromium.org/gerrit/25891
Reviewed-by: Benson Leung <bleung@chromium.org>
Commit-Ready: Andrew de los Reyes <adlr@chromium.org>
Tested-by: Andrew de los Reyes <adlr@chromium.org>
2 files changed