Rename HostResolverImpl -> HostResolverManager

Still filling the same role as before, implementing most of the logic
behind host resolution.  But since it no longer directly implements the
HostResolver interface, its name was confusing.

Bug: 934402
Change-Id: I3e9ca0133d3b68bf230257a0208bdadb6d7a09cd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1483691
Commit-Queue: Eric Orth <ericorth@chromium.org>
Reviewed-by: Asanka Herath <asanka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639089}
14 files changed