Migrate about_handler to BindOnce

Bug: 714018
Change-Id: I365b66d8017dfaa0d84d3dabddf4e11606b4228b
Reviewed-on: https://chromium-review.googlesource.com/1131320
Reviewed-by: David Benjamin <davidben@chromium.org>
Commit-Queue: Mark Pilgrim <pilgrim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573772}
1 file changed