[MacViews] Position modal sheets using ModalDialogHost.

ui/views/widget/native_widget_mac.h

 // Copyright 2014 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_VIEWS_WIDGET_NATIVE_WIDGET_MAC_H_
 #define UI_VIEWS_WIDGET_NATIVE_WIDGET_MAC_H_
 
 #include "ui/gfx/native_widget_types.h"
 #include "ui/views/widget/native_widget_private.h"
 
@@ skipping 18 matching lines @@
   // Return true if the delegate's modal type is window-modal. These display as
   // a native window "sheet", and have a different lifetime to regular windows.
   bool IsWindowModalSheet() const;
 
   // Deletes |bridge_| and informs |delegate_| that the native widget is
   // destroyed.
   // This is usually called from the NSWindowDelegate. A derived class can
   // override this method for an early hook into the native window teardown.
   virtual void OnWindowWillClose();
 
+  // Returns the vertical position that sheets should be anchored, relative to
+  // the top of the window.
+  virtual int SheetPositionY();
+
   // internal::NativeWidgetPrivate:
   void InitNativeWidget(const Widget::InitParams& params) override;
   NonClientFrameView* CreateNonClientFrameView() override;
   bool ShouldUseNativeFrame() const override;
   bool ShouldWindowContentsBeTransparent() const override;
   void FrameTypeChanged() override;
   Widget* GetWidget() override;
   const Widget* GetWidget() const override;
   gfx::NativeView GetNativeView() const override;
   gfx::NativeWindow GetNativeWindow() const override;
@@ skipping 88 matching lines @@
   scoped_ptr<BridgedNativeWidget> bridge_;
 
   Widget::InitParams::Ownership ownership_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeWidgetMac);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_NATIVE_WIDGET_MAC_H_