Migrate policy_conversions from DictionaryValue to Value

Also add safeguard checks as policy dump might be requested
by log upload job at times when not all services might be
available for the profile.

Bug: 863075
Change-Id: I45a88711c202800f89282dc0028e079bddb4324e
Reviewed-on: https://chromium-review.googlesource.com/1136533
Reviewed-by: Scott Chen <scottchen@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Commit-Queue: Denis Kuznetsov <antrim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575649}
3 files changed