Add input delay UKM.

This CL is to record input delay UKM which is defined as the duration
between the hardware timestamp and the start of event processing on the
main thread for the meaningful input.

UKM Privacy Review:
https://docs.google.com/document/d/1VQvmb3x7uGMmt2JvKt3_4zk1SPWHPB3yJSiyec7hY20

Bug: 1042004
Change-Id: I69eb91955f116e1f90b9b72a7d3dd13b449fa4ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2008436Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Commit-Queue: Hongbo Song <hbsong@google.com>
Cr-Commit-Position: refs/heads/master@{#736527}

third_party/blink/renderer/core/loader/interactive_detector.cc

@@ -5,6 +5,8 @@
 #include "third_party/blink/renderer/core/loader/interactive_detector.h"
 
 #include "base/time/default_tick_clock.h"
+#include "services/metrics/public/cpp/ukm_builders.h"
+#include "services/metrics/public/cpp/ukm_recorder.h"
 #include "third_party/blink/renderer/core/dom/document.h"
 #include "third_party/blink/renderer/core/dom/events/event.h"
 #include "third_party/blink/renderer/core/frame/local_frame.h"
@@ -228,6 +230,13 @@ void InteractiveDetector::HandleForInputDelay(
     input_delay_metrics_changed = true;
   }
 
+  // Record input delay UKM.
+  ukm::SourceId source_id = GetSupplementable()->UkmSourceID();
+  DCHECK_NE(source_id, ukm::kInvalidSourceId);
+  ukm::builders::InputEvent(source_id)
+      .SetInteractiveTiming_InputDelay(delay.InMilliseconds())
+      .Record(ukm::UkmRecorder::Get());
+
   UMA_HISTOGRAM_CUSTOM_TIMES(kHistogramInputDelay, delay,
                              base::TimeDelta::FromMilliseconds(1),
                              base::TimeDelta::FromSeconds(60), 50);

third_party/blink/renderer/core/loader/interactive_detector_test.cc

 // Copyright 2017 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 "components/ukm/test_ukm_recorder.h"
+#include "services/metrics/public/cpp/ukm_builders.h"
 
 #include "third_party/blink/renderer/core/loader/interactive_detector.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/blink/renderer/core/dom/document.h"
+#include "third_party/blink/renderer/core/dom/events/event.h"
 #include "third_party/blink/renderer/core/paint/first_meaningful_paint_detector.h"
 #include "third_party/blink/renderer/core/testing/dummy_page_holder.h"
 #include "third_party/blink/renderer/core/testing/page_test_base.h"
@@ -16,6 +19,8 @@
 
 namespace blink {
 
+using InputEvent = ukm::builders::InputEvent;
+
 class NetworkActivityCheckerForTest
     : public InteractiveDetector::NetworkActivityChecker {
  public:
@@ -598,4 +603,23 @@ TEST_F(InteractiveDetectorTest, LongTaskAfterTTIDoesNothing) {
   EXPECT_EQ(GetDetector()->GetInteractiveTime(), long_task_1_end_time);
 }
 
+TEST_F(InteractiveDetectorTest, RecordInputDelayUKM) {
+  ukm::TestAutoSetUkmRecorder test_ukm_recorder;
+  base::TimeDelta delay = base::TimeDelta::FromMilliseconds(10);
+  Event event;
+  event.SetTrusted(true);
+  event.SetType(event_type_names::kClick);
+  base::TimeTicks processing_start = Now() + delay;
+  base::TimeTicks event_platform_timestamp = Now();
+
+  GetDetector()->HandleForInputDelay(event, event_platform_timestamp,
+                                     processing_start);
+  auto entries = test_ukm_recorder.GetEntriesByName(InputEvent::kEntryName);
+  EXPECT_EQ(1ul, entries.size());
+  auto* entry = entries[0];
+  test_ukm_recorder.ExpectEntryMetric(
+      entry, InputEvent::kInteractiveTiming_InputDelayName,
+      delay.InMilliseconds());
+}
+
 }  // namespace blink

tools/metrics/ukm/ukm.xml

@@ -4141,6 +4141,23 @@ be describing additional metrics about the same event.
   </metric>
 </event>
 
+<event name="InputEvent">
+  <owner>hbsong@chromium.org</owner>
+  <summary>
+    Metrics associated with user input events. This event is recorded in Blink
+    and may not be recorded for the same page visits as events like PageLoad.
+    Consumers of this event's metrics should be aware of this when making
+    comparisons between InputEvent metrics and PageLoad metrics.
+  </summary>
+  <metric name="InteractiveTiming.InputDelay">
+    <summary>
+      Measures Input Delay, the duration between the hardware timestamp and the
+      start of event processing on the main thread for the meaningful input. In
+      ms. (go/FirstInputDelay)
+    </summary>
+  </metric>
+</event>
+
 <event name="Intervention.DocumentWrite.ScriptBlock" singular="True">
   <owner>bmcquade@chromium.org</owner>
   <summary>