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

chrome/browser/cocoa/browser_window_controller.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_BROWSER_WINDOW_CONTROLLER_H_
 #define CHROME_BROWSER_COCOA_BROWSER_WINDOW_CONTROLLER_H_
 
 // A class acting as the Objective-C controller for the Browser
 // object. Handles interactions between Cocoa and the cross-platform
 // code. Each window has a single toolbar and, by virtue of being a
@@ skipping 142 matching lines @@
 - (float)verticalOffsetForStatusBubble;
 
 // Show the bookmark bubble (e.g. user just clicked on the STAR)
 - (void)showBookmarkBubbleForURL:(const GURL&)url
                alreadyBookmarked:(BOOL)alreadyBookmarked;
 
 // Returns the (lazily created) window sheet controller of this window. Used
 // for the per-tab sheets.
 - (GTMWindowSheetController*)sheetController;
 
-- (void)attachConstrainedWindow:(ConstrainedWindowMac*)window;
+// Requests that |window| is opened as a per-tab sheet to the current tab.
+// Returns YES if the window became the active per-tab sheet of the current tab,
+// or NO if the current tab already has a per-tab sheet. If this returns NO,
+// the window's |Realize()| method will be called again when the curren sheet
+// disappears. The window should then call |attachConstrainedWindow:| again.
+- (BOOL)attachConstrainedWindow:(ConstrainedWindowMac*)window;
+
+// Closes the tab sheet |window| and potentially shows the next sheet in the
+// tab's sheet queue.
 - (void)removeConstrainedWindow:(ConstrainedWindowMac*)window;
 
 // Delegate method called when window is resized.
 - (void)windowDidResize:(NSNotification*)notification;
 
 @end
 
 
 @interface BrowserWindowController(TestingAPI)
 
@@ skipping 12 matching lines @@
 
 // Updates a bookmark sync UI item (expected to be a menu item).  This is
 // called every time the menu containing the sync UI item is displayed.
 - (void)updateSyncItem:(id)syncItem
            syncEnabled:(BOOL)syncEnabled
                 status:(SyncStatusUIHelper::MessageType)status;
 
 @end  // BrowserWindowController(TestingAPI)
 
 #endif  // CHROME_BROWSER_COCOA_BROWSER_WINDOW_CONTROLLER_H_