Prerender: avoid race condition with canceling prerender in test.

chrome/browser/prerender/prerender_browsertest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 #include <deque>
 #include <set>
 #include <string>
 #include <unordered_map>
 #include <utility>
@@ skipping 3276 matching lines @@
       "Prerender.websame_PrefetchTTFCP.Warm.Cacheable.Visible", 1);
   histogram_tester().ExpectUniqueSample(
       "Prerender.websame_PrefetchTTFCP.Warm.Cacheable.Visible", 1654, 1);
 }
 
 IN_PROC_BROWSER_TEST_F(PrerenderBrowserTest, FirstContentfulPaintTimingReuse) {
   GetPrerenderManager()->DisablePageLoadMetricsObserverForTesting();
   base::SimpleTestTickClock* clock = OverridePrerenderManagerTimeTicks();
 
   GURL url = embedded_test_server()->GetURL("/prerender/prerender_page.html");
+  base::RunLoop hanging_request_waiter;
+  BrowserThread::PostTask(BrowserThread::IO, FROM_HERE,
+                          base::Bind(&CreateHangingFirstRequestInterceptorOnIO,
+                                     url, GetTestPath("prerender_page.html"),
+                                     hanging_request_waiter.QuitClosure()));
   // As this load will be canceled, it is not waited for, and hence no
   // javascript is executed.
   DisableJavascriptCalls();
   PrerenderTestURL(url, FINAL_STATUS_CANCELLED, 0);
+  hanging_request_waiter.Run();
 
   // This prerender cancels and reuses the first.
   clock->Advance(base::TimeDelta::FromSeconds(1));
   base::TimeTicks load_start = clock->NowTicks();
   EnableJavascriptCalls();
   PrerenderTestURL(url, FINAL_STATUS_USED, 1);
   clock->Advance(base::TimeDelta::FromSeconds(1));
 
   NavigateToDestURL();
   PrerenderPageLoadMetricsObserver observer(GetPrerenderManager(),
@@ skipping 440 matching lines @@
       browser()->tab_strip_model()->GetActiveWebContents();
   bool display_test_result = false;
   ASSERT_TRUE(content::ExecuteScriptAndExtractBool(web_contents,
                                                    "DidDisplayReallyPass()",
                                                    &display_test_result));
   ASSERT_TRUE(display_test_result);
 }
 #endif  // !defined(DISABLE_NACL)
 
 }  // namespace prerender