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This change encapsulates |addrinfo| in an RAII class and abstracts the
implementation details of invoking |getaddrinfo| from callers. (The callers
still need to know how to use |hints| however).

One helper function moved from host_resolver_proc to the |AddressInfo|
class, and some massaging of error codes from host_resolver_proc was
also moved to address_info.cc.

The actual call to |getaddrinfo| is wrapped in a class with two virtual
calls (eponymously named |getaddrinfo| and |freeaddrinfo|) so that they
can be replaced in unit tests.

Unit tests are added for the code in address_info.cc.

Change-Id: Iada36ebbe0b783cd395f100c4e9d5753b5de2265
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1760461Reviewed-by: Eric Orth <ericorth@chromium.org>
Commit-Queue: Scott Sheehan <ssheehan@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#710863}