Migrate ExtensionDownloader away from base::Bind()

BUG=714018

Change-Id: Ia8ed733ab2d77eb6ac5672bf3ac846019a62e59f
Reviewed-on: https://chromium-review.googlesource.com/1066410
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#559973}
1 file changed