[net/dns] Test IPv6 support via UDP connect (measurement)
Network interface enumeration is expensive and requires absolutely no false negatives
in network change detection. In contrast bionic (Android libc) connects a UDP socket
to an IPv6 address which confirms that the kernel can route to such address.
This CL adds the UDP connect test to measure its performance compared to the probe.
BUG=223876
Review URL: https://chromiumcodereview.appspot.com/
13812002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@193421 0039d316-1c4b-4281-b951-d872f2087c98