GitLab

Currently HostResolverImpl tries to probe IPv6 support for every
Resolve() request, i.e. very often. The probe is implemented using
a dummy UDP socket. This doesn't look efficient because IPv6 state
doesn't change often.

Also this change will decrease frequency of the crash in the linked bug.
In that bug the root cause is that on OSX system certificate library may
close recently created file descriptors it doesn't own. Not creating
dummy UDP sockets very often will help to avoid hitting this bug in the
OS very often.

BUG=481163

Review URL: https://codereview.chromium.org/1138833003

Cr-Commit-Position: refs/heads/master@{#329885}