Left-align download item titles.

This was an oversight from switching from StyledLabel back to Label.

Bug: 1163862
Change-Id: Ie73be19702a8652e85df01f00e5e29f79ce82d48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2773956


Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#864951}