Improve performance of proxy resolver by tracing DNS dependencies.

net/proxy/proxy_resolver_mac.cc

Index: net/proxy/proxy_resolver_mac.cc
diff --git a/net/proxy/proxy_resolver_mac.cc b/net/proxy/proxy_resolver_mac.cc
index a5a05aff118b36462f58b80673b640be8d99e114..d452ef889a5bccc04bd9c768a3195c6e4d9b7f62 100644
--- a/net/proxy/proxy_resolver_mac.cc
+++ b/net/proxy/proxy_resolver_mac.cc
@@ -196,11 +196,6 @@ LoadState ProxyResolverMac::GetLoadState(RequestHandle request) const {
   return LOAD_STATE_IDLE;
 }
 
-LoadState ProxyResolverMac::GetLoadStateThreadSafe(
-    RequestHandle request) const {
-  return LOAD_STATE_IDLE;
-}
-
 void ProxyResolverMac::CancelSetPacScript() {
   NOTREACHED();
 }