Add WindowPinType property on arua::Window

ash/public/cpp/window_properties.h

 // Copyright 2017 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_PUBLIC_CPP_WINDOW_PROPERTIES_H_
 #define ASH_PUBLIC_CPP_WINDOW_PROPERTIES_H_
 
 #include <stdint.h>
 
 #include "ash/public/cpp/ash_public_export.h"
 #include "ash/public/cpp/shelf_types.h"
 #include "ui/base/class_property.h"
 
 namespace aura {
 template <typename T>
 using WindowProperty = ui::ClassProperty<T>;
 }
 
 namespace ash {
 
+namespace mojom {
+enum class WindowPinType;
+}
+
 // Shell-specific window property keys for use by ash and its clients.
 
 // Alphabetical sort.
 
 // If true (and the window is a panel), it's attached to its shelf item.
 ASH_PUBLIC_EXPORT extern const aura::WindowProperty<bool>* const
     kPanelAttachedKey;
 
 // A property key to store the type of a window's shelf item.
 ASH_PUBLIC_EXPORT extern const aura::WindowProperty<int32_t>* const
     kShelfItemTypeKey;
 
+// A property key to store ash::WindowPinType for a window.
+// When setting this property to PINNED or TRUSTED_PINNED, the window manager
+// will try to fullscreen the window and pin it on the top of the screen. If the
+// window manager failed to do it, the property will be restored to NONE. When
+// setting this property to NONE, the window manager will restore the window.
+ASH_PUBLIC_EXPORT extern const aura::WindowProperty<
+    ash::mojom::WindowPinType>* const kWindowPinTypeKey;
+
 // Alphabetical sort.
 
 }  // namespace ash
 
 #endif  // ASH_PUBLIC_CPP_WINDOW_PROPERTIES_H_