Store previous and current frame, copying current to previous after SYN.

BUG=chromium-os:38738
TEST=Previous frame contains touch info for last frame.

Change-Id: I8b972744835101a8c3a250eb6d218451ffebfae8
Reviewed-on: https://gerrit.chromium.org/gerrit/42874
Reviewed-by: Andrew de los Reyes <adlr@chromium.org>
Commit-Queue: Robert Flack <flackr@chromium.org>
Tested-by: Robert Flack <flackr@chromium.org>
4 files changed