DnsClient refactoring + features (timeout, suffix search, server rotation).

DnsClient::Request ==> DnsTransaction
DnsTransaction ==> DnsTransactionImpl
DnsClient ==> DnsTransactionFactory

BUG=109949
TEST=net_unittests --gtest_filter=Dns*


Review URL: http://codereview.chromium.org/9190031

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@119146 0039d316-1c4b-4281-b951-d872f2087c98
23 files changed