Reset drag state variables on mouse up

We need to reset the drag related variables
on regerdless of whether the mouse up was
preventDefaulted or not. Because after mouse up
there is no drag until the next mouse down.

BUG=308989

Review-Url: https://codereview.chromium.org/2042333006
Cr-Commit-Position: refs/heads/master@{#403694}
3 files changed