Use context from ContextHostResolver for DoH

Had to divorce some things in HostResolver from HostCache::Key since
different requests now have different context but the cache shouldn't
be keying on context (although in a separate CL, different contexts
will soon use separate caches entirely).  Jobs are now keyed on a
separate JobKey struct, and things are passed around by raw data
(hostname, query_type, etc) with HostCache::Key and JobKey generated
from that as needed rather than using any key type as a container of
request parameters.

Bug: 934402
Change-Id: Ic2d3ccd515456f25a9a09976f82dd7d277638efb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1535148
Commit-Queue: Eric Orth <[email protected]>
Reviewed-by: Matt Menke <[email protected]>
Cr-Commit-Position: refs/heads/master@{#651326}
8 files changed