[Prerender] first contentful paint histograms.

chrome/browser/prerender/prerender_test_utils.h

Index: chrome/browser/prerender/prerender_test_utils.h
diff --git a/chrome/browser/prerender/prerender_test_utils.h b/chrome/browser/prerender/prerender_test_utils.h
index dac536759737441a66807d202e570dbf7160fe08..9ee89cae8aeac59e571379c535063e2f0d574798 100644
--- a/chrome/browser/prerender/prerender_test_utils.h
+++ b/chrome/browser/prerender/prerender_test_utils.h
@@ -17,6 +17,7 @@
 #include "base/run_loop.h"
 #include "base/test/histogram_tester.h"
 #include "chrome/browser/external_protocol/external_protocol_handler.h"
+#include "chrome/browser/page_load_metrics/observers/prerender_page_load_metrics_observer.h"
 #include "chrome/browser/prerender/prerender_contents.h"
 #include "chrome/browser/prerender/prerender_manager.h"
 #include "chrome/browser/safe_browsing/test_safe_browsing_service.h"
@@ -237,6 +238,27 @@ class DestructionWaiter {
   DISALLOW_COPY_AND_ASSIGN(DestructionWaiter);
 };
 
+// Wait until a PrerenderManager has seen a first contentful paint.
+class FirstContentfulPaintManagerWaiter : public PrerenderManagerObserver {
+ public:
+  // Create and return a pointer to a |FirstContentfulPaintManagerWaiter|. The
+  // instance is owned by the |PrerenderManager|.
+  static FirstContentfulPaintManagerWaiter* Create(PrerenderManager* manager);
+
+  ~FirstContentfulPaintManagerWaiter() override;
+
+  void OnFirstContentfulPaint() override;
+
+  // Wait for a first contentful paint to be seen by our PrerenderManager.
+  void Wait();
+
+ private:
+  FirstContentfulPaintManagerWaiter();
+
+  std::unique_ptr<base::RunLoop> waiter_;
+  bool saw_fcp_;
+};

[pasko, 2016/12/20 19:33:34]

nit: DISALLOW_COPY_AND_ASSIGN?

[mattcary, 2016/12/21 17:08:58]

Done.

+
 // PrerenderContentsFactory that uses TestPrerenderContents.
 class TestPrerenderContentsFactory : public PrerenderContents::Factory {
  public:
@@ -363,6 +385,17 @@ class PrerenderInProcessBrowserTest : virtual public InProcessBrowserTest {
   DISALLOW_COPY_AND_ASSIGN(PrerenderInProcessBrowserTest);
 };
 
+// A test observer that allows the observed navigation start time to be set.
+class TestPrerenderPageLoadMetricsObserver
+    : public PrerenderPageLoadMetricsObserver {
+ public:
+  using PrerenderPageLoadMetricsObserver::PrerenderPageLoadMetricsObserver;

[pasko, 2016/12/20 19:33:34]

thanks for letting me know about inherited constructors :)

[mattcary, 2016/12/21 17:08:58]

Ack

I think it was actually from digit@ and notes from his C++ class...

+
+  void SetNavigationStartTo(base::TimeTicks ticks) {
+    SetNavigationStartTicksForTesting(ticks);

[pasko, 2016/12/20 19:33:34]

The only thing this class does is forwarding to this protected method, which
complicates reading the callsites. Can we make
PrerenderPageLoadMetricsObserver::SetNavigationStartTicksForTesting() public
instead?

[mattcary, 2016/12/21 17:08:59]

It seems to be common to hide testing code with protected, but it doesn't matter
much to me.

[pasko, 2016/12/21 18:39:09]

Ah, now I see where it is coming from. I think it is an important feature of the
suffix "ForTesting" to avoid extra overhead of subclassing.

[mattcary, 2016/12/22 10:49:07]

Acknowledged.

+  }
+};

[pasko, 2016/12/20 19:33:34]

nit: DISALLOW_COPY_AND_ASSIGN?

[mattcary, 2016/12/21 17:08:59]

Done.

+
 // Makes |url| respond to requests with the contents of |file|, counting the
 // number that start in |counter|.
 void CreateCountingInterceptorOnIO(