Report the duration of sampled tasks with histogram.

components/scheduler/renderer/task_duration_reporter_unittest.cc

+// 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 "components/scheduler/renderer/task_duration_reporter.h"
+
+#include "base/test/histogram_tester.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace scheduler {
+TEST(TaskDurationReporterTest, LoggingDuration) {
+  base::HistogramTester tester;
+
+  TaskDurationReporter task_duration_reporter;
+  for (int i = 1; i <= 101; ++i) {
+    base::TimeDelta duration = base::TimeDelta::FromMilliseconds(1);
+    if (i == 100) {
+      duration = base::TimeDelta::FromMilliseconds(2);
+    }
+    task_duration_reporter.ReportTaskDuration(duration);
+  }
+  tester.ExpectUniqueSample("RendererScheduler.TaskDuration", 2000, 1);
+}
+}