Plumb experiment flags through page_load_metrics and add a new observer

chrome/browser/page_load_metrics/observers/document_write_page_load_metrics_observer_unittest.cc

Index: chrome/browser/page_load_metrics/observers/document_write_page_load_metrics_observer_unittest.cc
diff --git a/chrome/browser/page_load_metrics/observers/document_write_page_load_metrics_observer_unittest.cc b/chrome/browser/page_load_metrics/observers/document_write_page_load_metrics_observer_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..1123e832eb61a38da5cfebd6ec49332c42c9e084
--- /dev/null
+++ b/chrome/browser/page_load_metrics/observers/document_write_page_load_metrics_observer_unittest.cc
@@ -0,0 +1,62 @@
+// Copyright 2016 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 "chrome/browser/page_load_metrics/observers/document_write_page_load_metrics_observer.h"
+#include "chrome/browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.h"
+#include "chrome/test/base/testing_browser_process.h"
+#include "third_party/WebKit/public/platform/WebLoadingBehaviorFlag.h"
+
+class DocumentWritePageLoadMetricsObserverTest
+    : public page_load_metrics::PageLoadMetricsObserverTestHarness {
+ protected:
+  void RegisterObservers(page_load_metrics::PageLoadTracker* tracker) override {
+    tracker->AddObserver(
+        make_scoped_ptr(new DocumentWritePageLoadMetricsObserver()));
+  }
+  void AssertNoHistogramsLogged() {
+    histogram_tester().ExpectTotalCount(
+        internal::kHistogramDocWriteParseStartToFirstContentfulPaint, 0);
+  }
+};
+
+TEST_F(DocumentWritePageLoadMetricsObserverTest, NoMetrics) {
+  AssertNoHistogramsLogged();
+}
+
+TEST_F(DocumentWritePageLoadMetricsObserverTest, PossiblePreload) {
+  base::TimeDelta contentful_paint = base::TimeDelta::FromMilliseconds(1);
+  page_load_metrics::PageLoadTiming timing;
+  timing.navigation_start = base::Time::FromDoubleT(1);
+  timing.first_contentful_paint = contentful_paint;
+  PopulateRequiredTimingFields(&timing);
+
+  page_load_metrics::PageLoadMetadata metadata;
+  metadata.behavior_flags |=
+      blink::WebLoadingBehaviorFlag::WebLoadingBehaviorDocumentWriteEvaluator;
+  NavigateAndCommit(GURL("https://www.google.com"));
+  SimulateTimingAndMetadataUpdate(timing, metadata);
+
+  NavigateAndCommit(GURL("https://www.example.com"));
+
+  histogram_tester().ExpectTotalCount(
+      internal::kHistogramDocWriteParseStartToFirstContentfulPaint, 1);
+  histogram_tester().ExpectBucketCount(
+      internal::kHistogramDocWriteParseStartToFirstContentfulPaint,
+      contentful_paint.InMilliseconds(), 1);
+}
+
+TEST_F(DocumentWritePageLoadMetricsObserverTest, NoPossiblePreload) {
+  base::TimeDelta contentful_paint = base::TimeDelta::FromMilliseconds(1);
+  page_load_metrics::PageLoadTiming timing;
+  timing.navigation_start = base::Time::FromDoubleT(1);
+  timing.first_contentful_paint = contentful_paint;
+  PopulateRequiredTimingFields(&timing);
+
+  page_load_metrics::PageLoadMetadata metadata;
+  NavigateAndCommit(GURL("https://www.google.com"));
+  SimulateTimingAndMetadataUpdate(timing, metadata);
+
+  NavigateAndCommit(GURL("https://www.example.com"));
+  AssertNoHistogramsLogged();
+}