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

ash/metrics/task_switch_metrics_recorder.h

 // 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.
 
 #ifndef ASH_METRICS_TASK_SWITCH_METRIC_RECORDER_H_
 #define ASH_METRICS_TASK_SWITCH_METRIC_RECORDER_H_
 
 #include <string>
 
 #include "ash/ash_export.h"
 #include "base/containers/scoped_ptr_hash_map.h"
 
 namespace ash {
 
 class TaskSwitchTimeTracker;
 
 // The TaskSwitchMetricsRecorder class records UMA metrics related to task
 // switching. The main purpose of the TaskSwitchMetricsRecorder is to track time
 // deltas between task switches and record histograms of the deltas.
 class ASH_EXPORT TaskSwitchMetricsRecorder {
  public:
   // Enumeration of the different user interfaces that could be the source of
   // a task switch. Note this is not necessarily comprehensive of all sources.
   enum TaskSwitchSource {
+    // Task switches between any two other sources. NOTE: This value should NOT

[tdanderson, 2015/06/02 15:56:12]

nit: suggested reword: "Task switches caused by any of the sources in this enum"
?

[bruthig, 2015/06/04 18:54:25]

Done.

+    // be used outside of this class.
+    kAny,
     // Task switches from selecting items in the app list.
     kAppList,
     // Task switches caused by selecting a window from overview mode which is
     // different from the previously-active window.
     kOverviewMode,
     // All task switches caused by shelf buttons, not including sub-menus.
     kShelf,
     // All task switches caused by the tab strip.
     kTabStrip,
     // Task switches caused by the WindowCycleController (ie Alt+Tab).
     kWindowCycleController
   };
 
   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).
   //
   // Will add an entry to |histogram_map_| when called for the first time for
   // each |task_switch_source| value.
+  //
+  // NOTE: A |task_switch_source| value of TaskSwitchSource::kAny should not be
+  // used and behavior is undefined if it is.

[tdanderson, 2015/06/02 15:56:12]

Include in the documentation of OnTaskSwitch() that it does two things: notifies
of a task switch corresponding to the specific source passed in, and also
notifies of an "any" task switch.

[bruthig, 2015/06/04 18:54:26]

Done.

   void OnTaskSwitch(TaskSwitchSource task_switch_source);
 
  private:
+  // Internal Implementation of OnTaskSwitch(TaskSwitchSource) that will accept

[tdanderson, 2015/06/02 15:56:11]

nit: lower-case i on implementation.

[bruthig, 2015/06/04 18:54:26]

Done.

+  // 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(
       TaskSwitchSource task_switch_source);
 
   // Adds a TaskSwitchTimeTracker to |histogram_map_| for the specified
   // |task_switch_source|. Behavior is undefined if a TaskSwitchTimeTracker
   // |histogram_map_| already has an entry for |task_switch_source|.
   void AddTaskSwitchTimeTracker(TaskSwitchSource task_switch_source);
 
   // Tracks TaskSwitchSource to TaskSwitchTimeTracker mappings. The
   // |histogram_map_| is populated on demand the first time a
   // TaskSwitchTimeTracker is needed for a given source.
   base::ScopedPtrHashMap<int, scoped_ptr<TaskSwitchTimeTracker>> histogram_map_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskSwitchMetricsRecorder);
 };
 
 }  // namespace ash
 
 #endif  // ASH_METRICS_TASK_SWITCH_METRIC_RECORDER_H_