GitLab

Do the following clean-ups in the webstore installer classes and its
callers:
- Convert base::Callback to base::RepeatingCallback/base::OnceCallback
- Convert base::Bind to base::BindRepeating/base::BindOnce
- Pass callbacks by value when an instance is retained

Bug: 714018

Change-Id: Ia55a04264ac528625c3f8664fd30607036945c24
Reviewed-on: https://chromium-review.googlesource.com/c/1391867Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619844}