MacViews: Reattach children of native windows when they are exposed.

ui/views/cocoa/widget_owner_nswindow_adapter.h

 // Copyright 2015 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_COCOA_WIDGET_OWNER_NSWINDOW_ADAPTER_H_
 #define UI_VIEWS_COCOA_WIDGET_OWNER_NSWINDOW_ADAPTER_H_
 
 #import "base/mac/scoped_nsobject.h"
 #include "base/macros.h"
 #import "ui/views/cocoa/bridged_native_widget_owner.h"
 
 @class NSView;
 @class NSWindow;
 @class WidgetOwnerNSWindowAdapterBridge;
 
 namespace views {
 
 // An adapter that allows a views::Widget to be owned by an NSWindow that is not
 // backed by another BridgedNativeWidget.
 class WidgetOwnerNSWindowAdapter : public BridgedNativeWidgetOwner {
  public:
   // Create an adapter that will own |child|, tying its lifetime with the
   // NSWindow containing |anchor_view|. The object is self-deleting, via a call
   // to RemoveChildWindow() made in child->OnWindowWillClose().
   WidgetOwnerNSWindowAdapter(BridgedNativeWidget* child, NSView* anchor_view);
 
   // Called when the owning window is closing.
   void OnWindowWillClose();
 
+  // Called when the owning window is hidden or shown.
+  void OnWindowDidChangeOcclusionState();
+
   // Overridden from BridgedNativeWidgetOwner:
   NSWindow* GetNSWindow() override;
   gfx::Vector2d GetChildWindowOffset() const override;
   bool IsVisibleParent() const override;
   void RemoveChildWindow(BridgedNativeWidget* child) override;
 
  private:
   // Self-deleting.
   ~WidgetOwnerNSWindowAdapter() override;
 
   BridgedNativeWidget* child_;  // Weak. Owned by its NativeWidgetMac.
   base::scoped_nsobject<NSView> anchor_view_;
   base::scoped_nsobject<NSWindow> anchor_window_;
   base::scoped_nsobject<WidgetOwnerNSWindowAdapterBridge> observer_bridge_;
 
   DISALLOW_COPY_AND_ASSIGN(WidgetOwnerNSWindowAdapter);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_COCOA_WIDGET_OWNER_NSWINDOW_ADAPTER_H_