Add FirstInputDelay integration test

This CL adds a test for FID that tests equality between the JS value and
the value reported in UKM and in UMA.

Change-Id: I00de8c947895700d86788ee4a95ea228458bb25f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2067077
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Reviewed-by: Steve Kobes <skobes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743212}

chrome/browser/page_load_metrics/integration_tests/first_input_delay_browsertest.cc

@@ -0,0 +1,56 @@
+// Copyright 2020 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/integration_tests/metric_integration_test.h"
+
+#include "base/test/trace_event_analyzer.h"
+#include "chrome/test/base/ui_test_utils.h"
+#include "services/metrics/public/cpp/ukm_builders.h"
+
+using base::Bucket;
+using base::Value;
+using trace_analyzer::Query;
+using trace_analyzer::TraceAnalyzer;
+using trace_analyzer::TraceEventVector;
+using ukm::builders::PageLoad;
+
+IN_PROC_BROWSER_TEST_F(MetricIntegrationTest, FirstInputDelay) {
+  LoadHTML(R"HTML(
+    <script>
+    runtest = async () => {
+      const observePromise = new Promise(resolve => {
+        new PerformanceObserver(e => {
+          e.getEntries().forEach(entry => {
+            const fid = entry.processingStart - entry.startTime;
+            resolve(fid);
+          })
+        }).observe({type: 'first-input', buffered: true});
+      });
+      return await observePromise;
+    };
+    </script>
+  )HTML");
+
+  StartTracing({"loading"});
+
+  content::SimulateMouseClickAt(web_contents(), 0,
+                                blink::WebMouseEvent::Button::kLeft,
+                                gfx::Point(10, 10));
+
+  // Check web perf API.
+  double expected_fid = EvalJs(web_contents(), "runtest()").ExtractDouble();
+  EXPECT_GT(expected_fid, 0.0);
+
+  ui_test_utils::NavigateToURL(browser(), GURL("about:blank"));
+
+  // Check UKM.
+  ExpectUKMPageLoadMetric(PageLoad::kInteractiveTiming_FirstInputDelay4Name,
+                          expected_fid);
+
+  // Check UMA.
+  auto samples = histogram_tester().GetAllSamples(
+      "PageLoad.InteractiveTiming.FirstInputDelay4");
+  EXPECT_EQ(1ul, samples.size());
+  EXPECT_EQ(samples[0], Bucket(expected_fid, 1));
+}

chrome/browser/page_load_metrics/integration_tests/sources.gni

@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 metric_integration_sources = [
+  "//chrome/browser/page_load_metrics/integration_tests/first_input_delay_browsertest.cc",
   "//chrome/browser/page_load_metrics/integration_tests/layout_instability_browsertest.cc",
   "//chrome/browser/page_load_metrics/integration_tests/metric_integration_test.cc",
   "//chrome/browser/page_load_metrics/integration_tests/metric_integration_test.h",