Fix LoadTimingBrowserTest.Proxy so it actually tests the proxy case.

After I changed the bypass policy for localhost, this test stopped routing through proxy.

Bug: 901896
Change-Id: I5f604865b60837143e7b2bc00c3dcbc9971c70c3
Reviewed-on: https://chromium-review.googlesource.com/c/1351145Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611874}

chrome/browser/net/load_timing_browsertest.cc

@@ -158,7 +158,8 @@ IN_PROC_BROWSER_TEST_F(LoadTimingBrowserTest, Proxy) {
   ProfileNetworkContextServiceFactory::GetForContext(browser()->profile())
       ->FlushProxyConfigMonitorForTesting();
 
-  GURL url = spawned_test_server()->GetURL("chunked?waitBeforeHeaders=100");
+  // This request will fail if it doesn't go through proxy.
+  GURL url("http://does.not.resolve.test/chunked?waitBeforeHeaders=100");
   ui_test_utils::NavigateToURL(browser(), url);
 
   TimingDeltas navigation_deltas;