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

ash/metrics/task_switch_metrics_recorder.h

Index: ash/metrics/task_switch_metrics_recorder.h
diff --git a/ash/metrics/task_switch_metrics_recorder.h b/ash/metrics/task_switch_metrics_recorder.h
index b2103be01d7a27a036cec32b1feaf9123f57db25..5a08757a6eb23aee24529de2dc8882ef5bb45b34 100644
--- a/ash/metrics/task_switch_metrics_recorder.h
+++ b/ash/metrics/task_switch_metrics_recorder.h
@@ -10,6 +10,10 @@
 #include "ash/ash_export.h"
 #include "base/containers/scoped_ptr_hash_map.h"
 
+namespace aura {
+class Window;
+}  // namespace aura
+
 namespace ash {
 
 class TaskSwitchTimeTracker;
@@ -27,6 +31,8 @@ class ASH_EXPORT TaskSwitchMetricsRecorder {
     // Task switches caused by selecting a window from overview mode which is
     // different from the previously-active window.
     kOverviewMode,
+    // TODO(bruthig):
+    kScreen,

[tdanderson, 2015/05/26 21:13:52]

Since these values are being used to indicate the UI surface where the task
switch took place, how about naming this kDesktop or kWorkspace?

[bruthig, 2015/06/03 21:59:31]

Done.

     // All task switches caused by shelf buttons, not including sub-menus.
     kShelf,
     // All task switches caused by the tab strip.
@@ -50,6 +56,9 @@ class ASH_EXPORT TaskSwitchMetricsRecorder {
   // each |task_switch_source| value.
   void OnTaskSwitch(TaskSwitchSource task_switch_source);
 
+  // Returns true if |window| is considered a task window.
+  bool IsATaskWindow(aura::Window* window) const;
+
  private:
   // Returns the TaskSwitchTimeTracker associated with the specified
   // |task_switch_source|. May return nullptr if mapping does not exist yet.