[net/dns] Initialize res_state in DnsConfigServicePosix.
[net/dns] Initialize res_state in DnsConfigServicePosix.

If there is no domain or search in /etc/resolv.conf
res_ninit() will return 0 ("no error") and set RES_INIT but it will
not reset res.dnsearch. Adding a memset to prevent non-UTF8 garbled
domain suffixes from crashing the NetLog.

BUG=115506
TEST=chrome --enable-async-dns # on Linux, and restart network


Review URL: http://codereview.chromium.org/9663048

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@126058 0039d316-1c4b-4281-b951-d872f2087c98

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