WebUI: cr-drawer, differeniate between cancel() and close()

Bug: 870732
Change-Id: I5cb196b87d339699be8bf5a2091e7e239d38b50d
Reviewed-on: https://chromium-review.googlesource.com/c/1289302
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Esmael El-Moslimany <aee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602203}
10 files changed