[net/dns] Add per-address-family histograms AsyncDNS.ResolveSuccess_FAMILY_* and per-qtype histograms AsyncDNS.TransactionSuccess_*.
Currently observed AsyncDNS.ResolveSuccess (duration of DnsTask) is almost twice as long as AsyncDNS.TransactionSuccess (duration of DnsTransaction). This could be attributed to dual-stack resolutions which involve two DnsTransactions, but at the same time the difference between DNS.ResolveSuccess_FAMILY_IPV4 and ..._UNSPEC (duration of ProcTask) is much less pronounced suggesting that SystemDNS resolves names on dual-stack hosts differently than AsyncDNS.
This measurement will allow us to determine how much of the observed overhead of DnsTask over DnsTransaction can be attributed to dual-stack lookups.
BUG=169257
Review URL: https://codereview.chromium.org/11783076
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@176137 0039d316-1c4b-4281-b951-d872f2087c98
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