Improve performance of proxy resolver by tracing DNS dependencies.

net/data/proxy_resolver_v8_tracing_unittest/dns_during_init.js

+var g_ips = [
+  dnsResolve('host1'),
+  dnsResolve('host2')
+];
+
+alert('Watsup');
+alert('Watsup2');
+
+function FindProxyForURL(url, host) {
+  // Note that host1 and host2 should not resolve using the same cache as was
+  // used for g_ips!
+  var ips = g_ips.concat([dnsResolve('host1'), dnsResolve('host2')]);
+  return 'PROXY ' + ips.join('-') + ':99';
+}