Added UMA statistics for changing the active window via click or touch events.

ash/metrics/task_switch_metrics_recorder_unittest.cc

Index: ash/metrics/task_switch_metrics_recorder_unittest.cc
diff --git a/ash/metrics/task_switch_metrics_recorder_unittest.cc b/ash/metrics/task_switch_metrics_recorder_unittest.cc
index 90a0db1fe07d08d86bc45db92d135d167d433e16..0b3d03ad414d4b59210713eaeb77c8d661b38e17 100644
--- a/ash/metrics/task_switch_metrics_recorder_unittest.cc
+++ b/ash/metrics/task_switch_metrics_recorder_unittest.cc
@@ -62,6 +62,20 @@ void TaskSwitchMetricsRecorderTest::TearDown() {
 
 }  // namespace
 
+// Verifies that the TaskSwitchMetricsRecorder::kDesktop source adds data to the
+// Ash.Desktop.TimeBetweenNavigateToTaskSwitches histogram.
+TEST_F(TaskSwitchMetricsRecorderTest, VerifyTaskSwitchesForDesktopAreRecorded) {
+  const std::string kHistogramName =
+      "Ash.Desktop.TimeBetweenNavigateToTaskSwitches";
+
+  OnTaskSwitch(TaskSwitchMetricsRecorder::kDesktop);
+  OnTaskSwitch(TaskSwitchMetricsRecorder::kDesktop);
+  histogram_tester_->ExpectTotalCount(kHistogramName, 1);
+
+  OnTaskSwitch(TaskSwitchMetricsRecorder::kDesktop);
+  histogram_tester_->ExpectTotalCount(kHistogramName, 2);
+}
+
 // Verifies that the TaskSwitchMetricsRecorder::kWindowCycleController source
 // adds data to the Ash.WindowCycleController.TimeBetweenTaskSwitches histogram.
 TEST_F(TaskSwitchMetricsRecorderTest,