Prerender: Add FCP histograms to nostate browsertests.

chrome/browser/prerender/prerender_nostate_prefetch_browsertest.cc

Index: chrome/browser/prerender/prerender_nostate_prefetch_browsertest.cc
diff --git a/chrome/browser/prerender/prerender_nostate_prefetch_browsertest.cc b/chrome/browser/prerender/prerender_nostate_prefetch_browsertest.cc
index 87ba6bb8c14583ca09157c6b5bf1fefbb0c0971c..3c6a2fc0d5f4b61f3efcf6037cbbde9c196a73eb 100644
--- a/chrome/browser/prerender/prerender_nostate_prefetch_browsertest.cc
+++ b/chrome/browser/prerender/prerender_nostate_prefetch_browsertest.cc
@@ -129,6 +129,35 @@ IN_PROC_BROWSER_TEST_F(NoStatePrefetchBrowserTest, PrefetchSimple) {
   test_prerender->WaitForLoads(0);
 }
 
+// Check that a prefetch followed by a load produces the approriate
+// histograms. Note that other histogram testing is done in
+// browser/page_load_metrics, in particular, testing the combinations of
+// Warm/Cold and Cacheable/NoCacheable.
+IN_PROC_BROWSER_TEST_F(NoStatePrefetchBrowserTest, PrefetchHistograms) {
+  RequestCounter main_counter;
+  CountRequestFor(kPrefetchPage, &main_counter);
+  RequestCounter script_counter;
+  CountRequestFor(kPrefetchScript, &script_counter);
+
+  PrefetchFromFile(kPrefetchPage, FINAL_STATUS_NOSTATE_PREFETCH_FINISHED);

[pasko, 2016/11/18 15:56:56]

PrefetchFromFile waits for Stop (i.e. when all prefetch requests are already
made), so request counters are not needed.

[mattcary, 2016/11/18 16:13:28]

Done.

+  main_counter.WaitForCount(1);
+  script_counter.WaitForCount(1);
+  histogram_tester().ExpectTotalCount(
+      "Prerender.websame_NoStatePrefetchTTFCP.Warm", 0);
+
+  test_utils::FirstContentfulPaintManagerWaiter* fcp_waiter =
+      test_utils::FirstContentfulPaintManagerWaiter::Create(
+          GetPrerenderManager());
+  ui_test_utils::NavigateToURL(
+      current_browser(), src_server()->GetURL(MakeAbsolute(kPrefetchPage)));
+  fcp_waiter->Wait();
+
+  histogram_tester().ExpectTotalCount(
+      "Prerender.websame_NoStatePrefetchTTFCP.Warm.Cacheable", 1);
+  histogram_tester().ExpectTotalCount(
+      "Prerender.websame_NoStatePrefetchResponseTypes", 2);
+}
+
 // Checks the prefetch of an img tag.
 IN_PROC_BROWSER_TEST_F(NoStatePrefetchBrowserTest, PrefetchImage) {
   RequestCounter image_counter;