Add NetworkIsolationKey support to HostResolverManager.

And a base::Feature to enable/disable respecting it.

This CL does not add NetworkIsolationKey support to HostResolvers
themselves, so when enabled in Chrome, the new base::Feature doesn't
actually do anything yet.


Bug: 997049
Change-Id: I86dd8a6c9bf4f00901cfeaa3aba120b8343e836d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1894175
Reviewed-by: Eric Orth <[email protected]>
Commit-Queue: Matt Menke <[email protected]>
Cr-Commit-Position: refs/heads/master@{#711784}
7 files changed