Added the Ash.Tab.TimeBetweenSwitchToExistingTabUserActions histogram to track time between tab swit

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 {
@@ skipping 74 matching lines @@
       "Ash.Shelf.TimeBetweenNavigateToTaskSwitches";
 
   OnTaskSwitch(TaskSwitchMetricsRecorder::kShelf);
   OnTaskSwitch(TaskSwitchMetricsRecorder::kShelf);
   histogram_tester_->ExpectTotalCount(kHistogramName, 1);
 
   OnTaskSwitch(TaskSwitchMetricsRecorder::kShelf);
   histogram_tester_->ExpectTotalCount(kHistogramName, 2);
 }
 
+// Verifies that the TaskSwitchMetricsRecorder::kTabStrip source adds data to
+// the Ash.Tab.TimeBetweenSwitchToExistingTabUserActions histogram.
+TEST_F(TaskSwitchMetricsRecorderTest,
+       VerifyTaskSwitchesFromTheTabStripAreRecorded) {
+  const std::string kHistogramName =
+      "Ash.Tab.TimeBetweenSwitchToExistingTabUserActions";
+
+  OnTaskSwitch(TaskSwitchMetricsRecorder::kTabStrip);
+  OnTaskSwitch(TaskSwitchMetricsRecorder::kTabStrip);
+  histogram_tester_->ExpectTotalCount(kHistogramName, 1);
+
+  OnTaskSwitch(TaskSwitchMetricsRecorder::kTabStrip);
+  histogram_tester_->ExpectTotalCount(kHistogramName, 2);
+}
+
 }  // namespace ash