[Mac] Avoid "adding unknown subview" warning.

chrome/browser/ui/cocoa/tabs/tab_window_controller.h

 // Copyright (c) 2012 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 CHROME_BROWSER_UI_COCOA_TABS_TAB_WINDOW_CONTROLLER_H_
 #define CHROME_BROWSER_UI_COCOA_TABS_TAB_WINDOW_CONTROLLER_H_
 
 // A class acting as the Objective-C window controller for a window that has
 // tabs which can be dragged around. Tabs can be re-arranged within the same
 // window or dragged into other TabWindowController windows. This class doesn't
 // know anything about the actual tab implementation or model, as that is fairly
 // application-specific. It only provides an API to be overridden by subclasses
 // to fill in the details.
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/mac/scoped_nsobject.h"
 
 @class FastResizeView;
 @class FocusTracker;
+@class NSVisualEffectView;
 @class TabStripView;
 @class TabView;
 
 @interface TabWindowController : NSWindowController<NSWindowDelegate> {
  @private
   // Wrapper view around web content, and the developer tools view.
   base::scoped_nsobject<FastResizeView> tabContentArea_;
   base::scoped_nsobject<NSView> tabStripBackgroundView_;
 
+  // Used to blur the titlebar. nil if window does not have titlebar.
+  base::scoped_nsobject<NSVisualEffectView> visualEffectView_;
+
   // The tab strip overlaps the titlebar of the window.
   base::scoped_nsobject<TabStripView> tabStripView_;
 
   // No views should be added directly to the root view. Views that overlap
   // the title bar should be added to the window's contentView. All other views
   // should be added to chromeContentView_. This allows tab dragging and
   // fullscreen logic to easily move the views that don't need special
   // treatment.
   base::scoped_nsobject<NSView> chromeContentView_;
 
@@ skipping 133 matching lines @@
 // Tells the tab strip to forget about this tab in preparation for it being
 // put into a different tab strip, such as during a drop on another window.
 - (void)detachTabView:(NSView*)view;
 
 // Called when the size of the window content area has changed. Override to
 // position specific views. Base class implementation does nothing.
 - (void)layoutSubviews;
 @end
 
 #endif  // CHROME_BROWSER_UI_COCOA_TABS_TAB_WINDOW_CONTROLLER_H_