Refactors maximize mode event handling into its own class

ash/wm/maximize_mode/maximize_mode_event_handler_aura.cc

+// Copyright 2016 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/maximize_mode/maximize_mode_event_handler_aura.h"
+
+#include "ash/shell.h"
+#include "ui/events/event.h"
+
+namespace ash {
+namespace wm {
+
+MaximizeModeEventHandlerAura::MaximizeModeEventHandlerAura() {
+  Shell::GetInstance()->AddPreTargetHandler(this);
+}
+
+MaximizeModeEventHandlerAura::~MaximizeModeEventHandlerAura() {
+  Shell::GetInstance()->RemovePreTargetHandler(this);
+}
+
+void MaximizeModeEventHandlerAura::OnTouchEvent(ui::TouchEvent* event) {
+  if (ToggleFullscreen(*event))
+    event->StopPropagation();
+}
+
+}  // namespace wm
+}  // namespace ash