Added Ash.TimeBetweenTaskSwitches to record time deltas between all recorded task switches.

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 177ff0807c260b2cce2b3a90ca1229a5d35a2b1e..c1ee339fc7e9cc497389228bc087e3463fc3ed46 100644
--- a/ash/metrics/task_switch_metrics_recorder.h
+++ b/ash/metrics/task_switch_metrics_recorder.h
@@ -27,6 +27,9 @@ class ASH_EXPORT TaskSwitchMetricsRecorder {
   // a task switch. Note this is not necessarily comprehensive of all sources.
   // TODO(bruthig): Convert enum format from kValue to VALUE.
   enum TaskSwitchSource {
+    // Task switches caused by any two sources in this enum. NOTE: This value
+    // should NOT be used outside of this class.
+    kAny,
     // Task switches from selecting items in the app list.
     kAppList,
     // Task switches caused by the user activating a task window by clicking or
@@ -46,19 +49,30 @@ class ASH_EXPORT TaskSwitchMetricsRecorder {
   TaskSwitchMetricsRecorder();
   virtual ~TaskSwitchMetricsRecorder();
 
-  // Notifies |this| that a "navigate to" task switch has occurred. A
-  // "navigate to" operation is defined by a task switch where the specific task
-  // that becomes active is user-predictable (ie Alt+Tab accelerator, launching
-  // a new window via the shelf, etc). Contrast to a "navigate away" operation
-  // which is defined as a user interaction that navigates away from a specified
-  // task and the next task that becomes active is likely not user-predictable
-  // (ie. closing or minimizing a window, closing a tab, etc).
+  // Notifies |this| that a "navigate to" task switch has occurred from the
+  // specified |task_switch_source|. The metrics associated with
+  // TaskSwitchSource::kAny source will be updated as well.
+  //
+  // NOTE: A |task_switch_source| value of TaskSwitchSource::kAny should not be
+  // used and behavior is undefined if it is.
+  //
+  // A "navigate to" operation is defined by a task switch where the specific
+  // task that becomes active is user-predictable (e.g., Alt+Tab accelerator,
+  // launching a new window via the shelf, etc). Contrast to a "navigate away"
+  // operation which is defined as a user interaction that navigates away from a
+  // specified task and the next task that becomes active is likely not
+  // user-predictable (e.g., closing or minimizing a window, closing a tab,
+  // etc).
   //
   // Will add an entry to |histogram_map_| when called for the first time for
   // each |task_switch_source| value.
   void OnTaskSwitch(TaskSwitchSource task_switch_source);
 
  private:
+  // Internal implementation of OnTaskSwitch(TaskSwitchSource) that will accept
+  // the TaskSwitchSource::kAny value.
+  void OnTaskSwitchInternal(TaskSwitchSource task_switch_source);
+
   // Returns the TaskSwitchTimeTracker associated with the specified
   // |task_switch_source|. May return nullptr if mapping does not exist yet.
   TaskSwitchTimeTracker* FindTaskSwitchTimeTracker(