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This is needed to separate out host resolutions made from different
sites. Also make PreconnectManager pass in the correct
NetworkIsolationKey. The two other consumers of the API currently pass
in empty NetworkIsolationKeys, and will be fixed in followup CLs.

Bug: 1021661
TBR: hashimoto@chromium.org, raymes@chromium.org, jam@chromium.org
Change-Id: I49d6d147f25dacce9d02112b2d0bfbe75a8a9b0b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1925136Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Oliver Chang <ochang@chromium.org>
Reviewed-by: Eric Roman <eroman@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718957}