[ash-md] Adds UMA items count and selection depth for Alt+Tab

ash/wm/window_cycle_controller.cc

 // Copyright 2014 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/wm/window_cycle_controller.h"
 
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/wm/mru_window_tracker.h"
 #include "ash/common/wm_shell.h"
 #include "ash/shell.h"
@@ skipping 78 matching lines @@
 void WindowCycleController::StartCycling() {
   MruWindowTracker::WindowList window_list =
       Shell::GetInstance()->mru_window_tracker()->BuildMruWindowList();
 
   active_window_before_window_cycle_ = GetActiveWindow(window_list);
 
   window_cycle_list_.reset(new WindowCycleList(window_list));
   event_handler_.reset(new WindowCycleEventFilter());
   cycle_start_time_ = base::Time::Now();
   WmShell::Get()->RecordUserMetricsAction(UMA_WINDOW_CYCLE);
+  UMA_HISTOGRAM_COUNTS_100("Ash.WindowCycleController.Items",
+                           window_list.size());
 }
 
 //////////////////////////////////////////////////////////////////////////////
 // WindowCycleController, private:
 
 void WindowCycleController::Step(Direction direction) {
   DCHECK(window_cycle_list_.get());
   window_cycle_list_->Step(direction);
 }
 
 void WindowCycleController::StopCycling() {
+  int depth = window_cycle_list_->current_index();

[tdanderson, 2016/06/24 19:25:56]

nit: no need for a local variable, just inline on line 123

[varkha, 2016/06/24 19:59:46]

|window_cycle_list_| goes away in the next line but I think I can move the UMA
statement here.

   window_cycle_list_.reset();
 
   WmWindow* active_window_after_window_cycle = GetActiveWindow(
       Shell::GetInstance()->mru_window_tracker()->BuildMruWindowList());
 
   // Remove our key event filter.
   event_handler_.reset();
   UMA_HISTOGRAM_MEDIUM_TIMES("Ash.WindowCycleController.CycleTime",
                              base::Time::Now() - cycle_start_time_);
+  UMA_HISTOGRAM_COUNTS_100("Ash.WindowCycleController.SelectionDepth",
+                           depth + 1);
 
   if (active_window_after_window_cycle != nullptr &&
       active_window_before_window_cycle_ != active_window_after_window_cycle) {
     Shell::GetInstance()
         ->metrics()
         ->task_switch_metrics_recorder()
         .OnTaskSwitch(TaskSwitchMetricsRecorder::WINDOW_CYCLE_CONTROLLER);
   }
   active_window_before_window_cycle_ = nullptr;
 }
 
 }  // namespace ash