Revert r333104: "Added UMA statistics for changing the active window via click or touch events."

ash/metrics/desktop_task_switch_metric_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_DESKTOP_TASK_SWITCH_METRIC_RECORDER_H_
-#define ASH_METRICS_DESKTOP_TASK_SWITCH_METRIC_RECORDER_H_
-
-#include "ash/ash_export.h"
-#include "base/macros.h"
-#include "ui/wm/public/activation_change_observer.h"
-
-namespace ash {
-
-class UserMetricsRecorder;
-
-// Tracks metrics for task switches caused by the user activating a task window
-// by clicking or tapping on it.
-class ASH_EXPORT DesktopTaskSwitchMetricRecorder
-    : public aura::client::ActivationChangeObserver {
- public:
-  explicit DesktopTaskSwitchMetricRecorder();
-  ~DesktopTaskSwitchMetricRecorder() override;
-
-  // aura::client::ActivationChangeObserver:
-  void OnWindowActivated(
-      aura::client::ActivationChangeObserver::ActivationReason reason,
-      aura::Window* gained_active,
-      aura::Window* lost_active) override;
-
- private:
-  // Tracks the last active task window.
-  aura::Window* last_active_task_window_;
-
-  DISALLOW_COPY_AND_ASSIGN(DesktopTaskSwitchMetricRecorder);
-};
-
-}  // namespace ash
-
-#endif  // ASH_METRICS_DESKTOP_TASK_SWITCH_METRIC_RECORDER_H_