Make WindowTree::SetModal() take the type.

ui/aura/window_port.h

Index: ui/aura/window_port.h
diff --git a/ui/aura/window_port.h b/ui/aura/window_port.h
index cc1ee5471588fca664cf796f38743235995bffe5..df3da59658480ccb6e46a05c7d63acf8168b41d2 100644
--- a/ui/aura/window_port.h
+++ b/ui/aura/window_port.h
@@ -66,9 +66,9 @@ class AURA_EXPORT WindowPort {
 
   // 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.