Mac: Only show one per-tab sheet at a time per tab.

chrome/browser/cocoa/constrained_window_mac.h

 // Copyright (c) 2009 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_COCOA_CONSTRAINED_WINDOW_MAC_H_
 #define CHROME_BROWSER_COCOA_CONSTRAINED_WINDOW_MAC_H_
 
 #import <Cocoa/Cocoa.h>
 
 #include "chrome/browser/tab_contents/constrained_window.h"
@@ skipping 107 matching lines @@
 
   // Overridden from ConstrainedWindow:
   virtual void CloseConstrainedWindow();
 
   // Returns the TabContents that constrains this Constrained Window.
   TabContents* owner() const { return owner_; }
 
   // Returns the window's delegate.
   ConstrainedWindowMacDelegate* delegate() { return delegate_; }
 
-  // Makes the constrained window visible, if it is not yet visible.
+  // Tells |controller_| that the sheet would like to be displayed.
   void Realize(BrowserWindowController* controller);
 
+  // Called by |controller_| to inform the sheet that it now is visible.
+  void SetVisible();
+
  private:
   friend class ConstrainedWindow;
 
   ConstrainedWindowMac(TabContents* owner,
                        ConstrainedWindowMacDelegate* delegate);
 
   // The TabContents that owns and constrains this ConstrainedWindow.
   TabContents* owner_;
 
   // Delegate that provides the contents of this constrained window.
   ConstrainedWindowMacDelegate* delegate_;
 
   // Controller of the window that contains this sheet.
   BrowserWindowController* controller_;
 
   DISALLOW_COPY_AND_ASSIGN(ConstrainedWindowMac);
 };
 
 #endif  // CHROME_BROWSER_COCOA_CONSTRAINED_WINDOW_MAC_H_