Convert onc::ReadDictionaryFromJson to use base::Value

This includes some partial conversion to base::Value in onc_utils.cc,
as part of a long term effort to convert network config and ONC code
to non deprecated base::Value patterns.

Bug: 651157
Change-Id: Ic0456f9221fedaf95a78ce670af9f4be4bc95ad1
Reviewed-on: https://chromium-review.googlesource.com/1144196
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577997}
12 files changed