Add "time to first text paint" to PageLoadMetrics system

This adds PageLoad.Timing2.NavigationToFirstTextPaint(.BG) UMA histogram which
measures the time between navigation start to first non-blank text paint.

BUG=520410
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1376643002

Cr-Commit-Position: refs/heads/master@{#352770}

6 files changed, 40 insertions, 3 deletions

diff --git a/components/page_load_metrics/browser/metrics_web_contents_observer.cc b/components/page_load_metrics/browser/metrics_web_contents_observer.cc
index df37a05..2961f1e 100644
--- a/components/page_load_metrics/browser/metrics_web_contents_observer.cc
+++ b/components/page_load_metrics/browser/metrics_web_contents_observer.cc
@@ -146,7 +146,15 @@ void PageLoadTracker::RecordTimingHistograms() {
       RecordEvent(PAGE_LOAD_SUCCESSFUL_FIRST_LAYOUT_BACKGROUND);
     }
   }
-
+  if (!timing_.first_text_paint.is_zero()) {
+    if (timing_.first_text_paint < background_delta) {
+      PAGE_LOAD_HISTOGRAM("PageLoad.Timing2.NavigationToFirstTextPaint",
+                          timing_.first_text_paint);
+    } else {
+      PAGE_LOAD_HISTOGRAM("PageLoad.Timing2.NavigationToFirstTextPaint.BG",
+                          timing_.first_text_paint);
+    }
+  }
 }
 
 void PageLoadTracker::RecordEvent(PageLoadEvent event) {
diff --git a/components/page_load_metrics/browser/metrics_web_contents_observer_unittest.cc b/components/page_load_metrics/browser/metrics_web_contents_observer_unittest.cc
index 147f094..fd06574 100644
--- a/components/page_load_metrics/browser/metrics_web_contents_observer_unittest.cc
+++ b/components/page_load_metrics/browser/metrics_web_contents_observer_unittest.cc
@@ -24,6 +24,8 @@ const char kDefaultTestUrl2[] = "https://whatever.com";
 
 const char kHistogramNameFirstLayout[] =
     "PageLoad.Timing2.NavigationToFirstLayout";
+const char kHistogramNameFirstTextPaint[] =
+    "PageLoad.Timing2.NavigationToFirstTextPaint";
 const char kHistogramNameDomContent[] =
     "PageLoad.Timing2.NavigationToDOMContentLoadedEventFired";
 const char kHistogramNameLoad[] =
@@ -31,6 +33,8 @@ const char kHistogramNameLoad[] =
 
 const char kBGHistogramNameFirstLayout[] =
     "PageLoad.Timing2.NavigationToFirstLayout.BG";
+const char kBGHistogramNameFirstTextPaint[] =
+    "PageLoad.Timing2.NavigationToFirstTextPaint.BG";
 const char kBGHistogramNameDomContent[] =
     "PageLoad.Timing2.NavigationToDOMContentLoadedEventFired.BG";
 const char kBGHistogramNameLoad[] =
@@ -55,6 +59,7 @@ class MetricsWebContentsObserverTest
     histogram_tester_.ExpectTotalCount(kHistogramNameDomContent, 0);
     histogram_tester_.ExpectTotalCount(kHistogramNameLoad, 0);
     histogram_tester_.ExpectTotalCount(kHistogramNameFirstLayout, 0);
+    histogram_tester_.ExpectTotalCount(kHistogramNameFirstTextPaint, 0);
   }
 
  protected:
@@ -141,6 +146,7 @@ TEST_F(MetricsWebContentsObserverTest, SamePageNoTriggerUntilTrueNavCommit) {
   histogram_tester_.ExpectTotalCount(kHistogramNameFirstLayout, 1);
   histogram_tester_.ExpectBucketCount(kHistogramNameFirstLayout,
                                       first_layout.InMilliseconds(), 1);
+  histogram_tester_.ExpectTotalCount(kHistogramNameFirstTextPaint, 0);
 }
 
 TEST_F(MetricsWebContentsObserverTest, SingleMetricAfterCommit) {
@@ -168,12 +174,14 @@ TEST_F(MetricsWebContentsObserverTest, SingleMetricAfterCommit) {
   histogram_tester_.ExpectTotalCount(kHistogramNameFirstLayout, 1);
   histogram_tester_.ExpectBucketCount(kHistogramNameFirstLayout,
                                       first_layout.InMilliseconds(), 1);
+  histogram_tester_.ExpectTotalCount(kHistogramNameFirstTextPaint, 0);
 }
 
 TEST_F(MetricsWebContentsObserverTest, MultipleMetricsAfterCommits) {
   base::TimeDelta first_layout_1 = base::TimeDelta::FromMilliseconds(1);
   base::TimeDelta first_layout_2 = base::TimeDelta::FromMilliseconds(20);
   base::TimeDelta response = base::TimeDelta::FromMilliseconds(10);
+  base::TimeDelta first_text_paint = base::TimeDelta::FromMilliseconds(30);
   base::TimeDelta dom_content = base::TimeDelta::FromMilliseconds(40);
   base::TimeDelta load = base::TimeDelta::FromMilliseconds(100);
 
@@ -181,6 +189,7 @@ TEST_F(MetricsWebContentsObserverTest, MultipleMetricsAfterCommits) {
   timing.navigation_start = base::Time::FromDoubleT(1);
   timing.first_layout = first_layout_1;
   timing.response_start = response;
+  timing.first_text_paint = first_text_paint;
   timing.dom_content_loaded_event_start = dom_content;
   timing.load_event_start = load;
 
@@ -212,6 +221,10 @@ TEST_F(MetricsWebContentsObserverTest, MultipleMetricsAfterCommits) {
   histogram_tester_.ExpectBucketCount(kHistogramNameFirstLayout,
                                       first_layout_2.InMilliseconds(), 1);
 
+  histogram_tester_.ExpectTotalCount(kHistogramNameFirstTextPaint, 1);
+  histogram_tester_.ExpectBucketCount(kHistogramNameFirstTextPaint,
+                                      first_text_paint.InMilliseconds(), 1);
+
   histogram_tester_.ExpectTotalCount(kHistogramNameDomContent, 1);
   histogram_tester_.ExpectBucketCount(kHistogramNameDomContent,
                                       dom_content.InMilliseconds(), 1);
@@ -252,10 +265,12 @@ TEST_F(MetricsWebContentsObserverTest, BackgroundDifferentHistogram) {
   histogram_tester_.ExpectTotalCount(kBGHistogramNameFirstLayout, 1);
   histogram_tester_.ExpectBucketCount(kBGHistogramNameFirstLayout,
                                       first_layout.InMilliseconds(), 1);
+  histogram_tester_.ExpectTotalCount(kBGHistogramNameFirstTextPaint, 0);
 
   histogram_tester_.ExpectTotalCount(kHistogramNameDomContent, 0);
   histogram_tester_.ExpectTotalCount(kHistogramNameLoad, 0);
   histogram_tester_.ExpectTotalCount(kHistogramNameFirstLayout, 0);
+  histogram_tester_.ExpectTotalCount(kHistogramNameFirstTextPaint, 0);
 }
 
 TEST_F(MetricsWebContentsObserverTest, OnlyBackgroundLaterEvents) {
@@ -278,6 +293,7 @@ TEST_F(MetricsWebContentsObserverTest, OnlyBackgroundLaterEvents) {
   observer_->WasHidden();
   observer_->WasShown();
   timing.first_layout = base::TimeDelta::FromSeconds(3);
+  timing.first_text_paint = base::TimeDelta::FromSeconds(4);
   observer_->OnMessageReceived(
       PageLoadMetricsMsg_TimingUpdated(observer_->routing_id(), timing),
       web_contents()->GetMainFrame());
@@ -290,6 +306,10 @@ TEST_F(MetricsWebContentsObserverTest, OnlyBackgroundLaterEvents) {
   histogram_tester_.ExpectTotalCount(kBGHistogramNameFirstLayout, 1);
   histogram_tester_.ExpectBucketCount(kBGHistogramNameFirstLayout,
                                       timing.first_layout.InMilliseconds(), 1);
+  histogram_tester_.ExpectTotalCount(kBGHistogramNameFirstTextPaint, 1);
+  histogram_tester_.ExpectBucketCount(kBGHistogramNameFirstTextPaint,
+                                      timing.first_text_paint.InMilliseconds(),
+                                      1);
 
   histogram_tester_.ExpectTotalCount(kHistogramNameDomContent, 1);
   histogram_tester_.ExpectBucketCount(
@@ -297,6 +317,7 @@ TEST_F(MetricsWebContentsObserverTest, OnlyBackgroundLaterEvents) {
       timing.dom_content_loaded_event_start.InMilliseconds(), 1);
   histogram_tester_.ExpectTotalCount(kHistogramNameLoad, 0);
   histogram_tester_.ExpectTotalCount(kHistogramNameFirstLayout, 0);
+  histogram_tester_.ExpectTotalCount(kHistogramNameFirstTextPaint, 0);
 }
 
 TEST_F(MetricsWebContentsObserverTest, DontBackgroundQuickerLoad) {
@@ -336,6 +357,7 @@ TEST_F(MetricsWebContentsObserverTest, DontBackgroundQuickerLoad) {
   histogram_tester_.ExpectTotalCount(kHistogramNameFirstLayout, 1);
   histogram_tester_.ExpectBucketCount(kHistogramNameFirstLayout,
                                       first_layout.InMilliseconds(), 1);
+  histogram_tester_.ExpectTotalCount(kHistogramNameFirstTextPaint, 0);
 }
 
 TEST_F(MetricsWebContentsObserverTest, FailProvisionalLoad) {
diff --git a/components/page_load_metrics/common/page_load_metrics_messages.h b/components/page_load_metrics/common/page_load_metrics_messages.h
index 466e244..0ad0d67 100644
--- a/components/page_load_metrics/common/page_load_metrics_messages.h
+++ b/components/page_load_metrics/common/page_load_metrics_messages.h
@@ -18,6 +18,7 @@ IPC_STRUCT_TRAITS_BEGIN(page_load_metrics::PageLoadTiming)
   IPC_STRUCT_TRAITS_MEMBER(dom_content_loaded_event_start)
   IPC_STRUCT_TRAITS_MEMBER(load_event_start)
   IPC_STRUCT_TRAITS_MEMBER(first_layout)
+  IPC_STRUCT_TRAITS_MEMBER(first_text_paint)
 IPC_STRUCT_TRAITS_END()
 
 // Sent from renderer to browser process when the PageLoadTiming for the
diff --git a/components/page_load_metrics/common/page_load_timing.cc b/components/page_load_metrics/common/page_load_timing.cc
index 781048e..0af13ea 100644
--- a/components/page_load_metrics/common/page_load_timing.cc
+++ b/components/page_load_metrics/common/page_load_timing.cc
@@ -16,13 +16,15 @@ bool PageLoadTiming::operator==(const PageLoadTiming& other) const {
          dom_content_loaded_event_start ==
              other.dom_content_loaded_event_start &&
          load_event_start == other.load_event_start &&
-         first_layout == other.first_layout;
+         first_layout == other.first_layout &&
+         first_text_paint == other.first_text_paint;
 }
 
 bool PageLoadTiming::IsEmpty() const {
   return navigation_start.is_null() && response_start.is_zero() &&
          dom_content_loaded_event_start.is_zero() &&
-         load_event_start.is_zero() && first_layout.is_zero();
+         load_event_start.is_zero() && first_layout.is_zero() &&
+         first_text_paint.is_zero();
 }
 
 }  // namespace page_load_metrics
diff --git a/components/page_load_metrics/common/page_load_timing.h b/components/page_load_metrics/common/page_load_timing.h
index 80a9701..f5a94ff 100644
--- a/components/page_load_metrics/common/page_load_timing.h
+++ b/components/page_load_metrics/common/page_load_timing.h
@@ -38,6 +38,9 @@ struct PageLoadTiming {
   // Time when the first layout is completed.
   base::TimeDelta first_layout;
 
+  // Time when the first non-blank text is painted.
+  base::TimeDelta first_text_paint;
+
   // If you add additional members, also be sure to update operator==,
   // page_load_metrics_messages.h, and IsEmpty().
 };
diff --git a/components/page_load_metrics/renderer/metrics_render_frame_observer.cc b/components/page_load_metrics/renderer/metrics_render_frame_observer.cc
index 7d06f9a..9d41dd3 100644
--- a/components/page_load_metrics/renderer/metrics_render_frame_observer.cc
+++ b/components/page_load_metrics/renderer/metrics_render_frame_observer.cc
@@ -112,6 +112,7 @@ PageLoadTiming MetricsRenderFrameObserver::GetTiming() const {
       ClampDelta(perf.domContentLoadedEventStart(), start);
   timing.load_event_start = ClampDelta(perf.loadEventStart(), start);
   timing.first_layout = ClampDelta(perf.firstLayout(), start);
+  timing.first_text_paint = ClampDelta(perf.firstTextPaint(), start);
   return timing;
 }