Migrate simple ash Shell metrics users.

ash/metrics/desktop_task_switch_metric_recorder.cc

 // 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.
 
 #include "ash/metrics/desktop_task_switch_metric_recorder.h"
 
-#include "ash/metrics/user_metrics_recorder.h"
+#include "ash/common/wm_shell.h"
 #include "ash/shell.h"
 #include "ash/wm/window_util.h"
 #include "ui/wm/public/activation_client.h"
 
 namespace ash {
 
 DesktopTaskSwitchMetricRecorder::DesktopTaskSwitchMetricRecorder()
     : last_active_task_window_(nullptr) {
   Shell::GetInstance()->activation_client()->AddObserver(this);
 }
 
 DesktopTaskSwitchMetricRecorder::~DesktopTaskSwitchMetricRecorder() {
   Shell::GetInstance()->activation_client()->RemoveObserver(this);
 }
 
 void DesktopTaskSwitchMetricRecorder::OnWindowActivated(
     aura::client::ActivationChangeObserver::ActivationReason reason,
     aura::Window* gained_active,
     aura::Window* lost_active) {
   if (gained_active && wm::IsWindowUserPositionable(gained_active)) {
     if (last_active_task_window_ != gained_active &&
         reason == aura::client::ActivationChangeObserver::ActivationReason::
                       INPUT_EVENT) {
-      Shell::GetInstance()->metrics()->RecordUserMetricsAction(
-          UMA_DESKTOP_SWITCH_TASK);
+      WmShell::Get()->RecordUserMetricsAction(UMA_DESKTOP_SWITCH_TASK);
     }
     last_active_task_window_ = gained_active;
   }
 }
 
 }  // namespace ash