Downloads: Fixed a crash on sharing

In certain devices, android fails to find an activity for launching the
share intent, which results in a crash. We should catch those exceptions.

Bug: 914816
Change-Id: I44e8dc7e64ca536e2138facf677b6de5e88e8d3c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1556456
Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#648849}