Added metrics to track the time between task switches done via the shelf.

ash/metrics/task_switch_metrics_recorder_unittest.cc

+// Copyright 2015 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 "ash/metrics/task_switch_metrics_recorder.h"
+
+#include "base/test/histogram_tester.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace ash {
+namespace {
+
+// Test fixture for the TaskSwitchMetricsRecorder class.
+class TaskSwitchMetricsRecorderTest : public testing::Test {
+ public:
+  TaskSwitchMetricsRecorderTest();
+  ~TaskSwitchMetricsRecorderTest() override;
+
+  // Wrapper to the test targets OnTaskSwitch(TaskSwitchSource) method.
+  void OnTaskSwitch(
+      TaskSwitchMetricsRecorder::TaskSwitchSource task_switch_source);
+
+  // testing::Test:
+  void SetUp() override;
+  void TearDown() override;
+
+ protected:
+  // Used to verify recorded data.
+  scoped_ptr<base::HistogramTester> histogram_tester_;
+
+  // The test target.
+  scoped_ptr<TaskSwitchMetricsRecorder> task_switch_metrics_recorder_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TaskSwitchMetricsRecorderTest);
+};
+
+TaskSwitchMetricsRecorderTest::TaskSwitchMetricsRecorderTest() {
+}
+
+TaskSwitchMetricsRecorderTest::~TaskSwitchMetricsRecorderTest() {
+}
+
+void TaskSwitchMetricsRecorderTest::OnTaskSwitch(
+    TaskSwitchMetricsRecorder::TaskSwitchSource task_switch_source) {
+  task_switch_metrics_recorder_->OnTaskSwitch(task_switch_source);
+}
+
+void TaskSwitchMetricsRecorderTest::SetUp() {
+  testing::Test::SetUp();
+
+  histogram_tester_.reset(new base::HistogramTester());
+  task_switch_metrics_recorder_.reset(new TaskSwitchMetricsRecorder());
+}
+
+void TaskSwitchMetricsRecorderTest::TearDown() {
+  testing::Test::TearDown();
+
+  histogram_tester_.reset();
+  task_switch_metrics_recorder_.reset();
+}
+
+}  // namespace
+
+// Verifies that the TaskSwitchMetricsRecorder::kShelf source adds data to the
+// Ash.Shelf.TimeBetweenNavigateToTaskSwitches histogram.
+TEST_F(TaskSwitchMetricsRecorderTest,
+       VerifyTaskSwitchesFromTheShelfAreRecorded) {
+  const std::string kHistogramName =
+      "Ash.Shelf.TimeBetweenNavigateToTaskSwitches";
+
+  OnTaskSwitch(TaskSwitchMetricsRecorder::kShelf);
+  OnTaskSwitch(TaskSwitchMetricsRecorder::kShelf);
+  histogram_tester_->ExpectTotalCount(kHistogramName, 1);
+
+  OnTaskSwitch(TaskSwitchMetricsRecorder::kShelf);
+  histogram_tester_->ExpectTotalCount(kHistogramName, 2);
+}
+
+}  // namespace ash