Added UMA statistics for changing the active window via click or touch events.

ash/metrics/screen_event_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_SCREEN_EVENT_TASK_SWITCH_METRIC_RECORDER_H_
+#define ASH_METRICS_SCREEN_EVENT_TASK_SWITCH_METRIC_RECORDER_H_
+
+#include "ash/ash_export.h"
+#include "base/macros.h"
+#include "ui/wm/core/window_activation_pre_target_handler_observer.h"
+#include "ui/wm/public/activation_change_observer.h"
+
+namespace aura {
+class Window;
+}  // namespace aura
+
+namespace ash {
+
+class UserMetricsRecorder;
+
+class ASH_EXPORT ScreenEventTaskSwitchMetricRecorder
+    : public wm::WindowActivationPreTargetHandlerObserver {
+ public:
+  explicit ScreenEventTaskSwitchMetricRecorder(
+      UserMetricsRecorder* user_metrics_recorder);
+  ~ScreenEventTaskSwitchMetricRecorder() override;
+
+  // wm::WindowActivationPreTargetHandlerObserver:
+  void BeforeWindowActivatedByPreTargetHandler() override;
+  void OnWindowActivatedByPreTargetHandler(aura::Window* gained_active,
+                                           aura::Window* lost_active) override;
+
+ private:
+  UserMetricsRecorder* user_metrics_recorder_;
+  aura::Window* active_window_before_activation_ = nullptr;

[tdanderson, 2015/05/26 21:13:52]

initialize to null in constructor

[bruthig, 2015/06/03 21:59:31]

Done.

+
+  DISALLOW_COPY_AND_ASSIGN(ScreenEventTaskSwitchMetricRecorder);
+};
+
+}  // namespace ash
+
+#endif  // ASH_METRICS_SCREEN_EVENT_TASK_SWITCH_METRIC_RECORDER_H_