Don't preresolve DNS if a fixed proxy configuration is in place.

net/proxy/proxy_service.h

Index: net/proxy/proxy_service.h
diff --git a/net/proxy/proxy_service.h b/net/proxy/proxy_service.h
index 69aaf46c13b087311be171f505904febdb7a7425..18e23ec04f0fcf51ea4f0d95dd53e0849684c511 100644
--- a/net/proxy/proxy_service.h
+++ b/net/proxy/proxy_service.h
@@ -123,13 +123,14 @@ class NET_EXPORT ProxyService : public NetworkChangeNotifier::IPAddressObserver,
   //   3.  named proxy
   //
   // Profiling information for the request is saved to |net_log| if non-NULL.
-  int ResolveProxy(const GURL& url,
-                   int load_flags,
-                   ProxyInfo* results,
-                   const net::CompletionCallback& callback,
-                   PacRequest** pac_request,
-                   NetworkDelegate* network_delegate,
-                   const BoundNetLog& net_log);
+  // This method is virtual for unit testing.
+  virtual int ResolveProxy(const GURL& url,
+                           int load_flags,
+                           ProxyInfo* results,
+                           const net::CompletionCallback& callback,
+                           PacRequest** pac_request,
+                           NetworkDelegate* network_delegate,
+                           const BoundNetLog& net_log);
 
   // This method is called after a failure to connect or resolve a host name.
   // It gives the proxy service an opportunity to reconsider the proxy to use.
@@ -177,7 +178,8 @@ class NET_EXPORT ProxyService : public NetworkChangeNotifier::IPAddressObserver,
                      NetworkDelegate* network_delegate);
 
   // Call this method with a non-null |pac_request| to cancel the PAC request.
-  void CancelPacRequest(PacRequest* pac_request);
+  // This method is virtual for unit testing.
+  virtual void CancelPacRequest(PacRequest* pac_request);
 
   // Returns the LoadState for this |pac_request| which must be non-NULL.
   LoadState GetLoadState(const PacRequest* pac_request) const;