Make WindowTree::SetModal() take the type.

ui/aura/window_port.h

 // 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.
 
 #ifndef UI_AURA_WINDOW_PORT_H_
 #define UI_AURA_WINDOW_PORT_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 48 matching lines @@
                                  const gfx::Rect& new_bounds) = 0;
 
   // Called before a property is changed. The return value from this is supplied
   // into OnPropertyChanged() so that WindowPort may pass data between the two
   // calls.
   virtual std::unique_ptr<ui::PropertyData> OnWillChangeProperty(
       const void* key) = 0;
 
   // Called after a property changes, but before observers are notified. |data|
   // is the return value from OnWillChangeProperty().
-  virtual void OnPropertyChanged(
-      const void* key,
-      std::unique_ptr<ui::PropertyData> data) = 0;
+  virtual void OnPropertyChanged(const void* key,
+                                 int64_t old_value,
+                                 std::unique_ptr<ui::PropertyData> data) = 0;
 
  protected:
   // Returns the WindowPort associated with a Window.
   static WindowPort* Get(Window* window);
 
   // Returns the ObserverList of a Window.
   static base::ObserverList<WindowObserver, true>* GetObservers(Window* window);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_PORT_H_