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

chrome/browser/cocoa/browser_window_controller.mm

 // 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.
 
 #include <Carbon/Carbon.h>
 
 #include "app/l10n_util_mac.h"
 #include "base/mac_util.h"
 #include "base/scoped_nsdisable_screen_updates.h"
 #import "base/scoped_nsobject.h"
@@ skipping 248 matching lines @@
   statusBubble_ = NULL;
   // We can't actually use |-autorelease| here because there's an embedded
   // run loop in the |-performClose:| which contains its own autorelease pool.
   // Instead we call it after a zero-length delay, which gets us back
   // to the main event loop.
   [self performSelector:@selector(autorelease)
              withObject:nil
              afterDelay:0];
 }
 
-- (void)attachConstrainedWindow:(ConstrainedWindowMac*)window {
-  [tabStripController_ attachConstrainedWindow:window];
+- (BOOL)attachConstrainedWindow:(ConstrainedWindowMac*)window {
+  return [tabStripController_ attachConstrainedWindow:window];
 }
 
 - (void)removeConstrainedWindow:(ConstrainedWindowMac*)window {
   [tabStripController_ removeConstrainedWindow:window];
 }
 
 // Called when the user wants to close a window or from the shutdown process.
 // The Browser object is in control of whether or not we're allowed to close. It
 // may defer closing due to several states, such as onUnload handlers needing to
 // be fired. If closing is deferred, the Browser will handle the processing
@@ skipping 1331 matching lines @@
   if (frameOverlayInactiveImage) {
     [theme setValue:frameOverlayInactiveImage
        forAttribute:@"overlay"
               style:GTMThemeStyleWindow
               state:GTMThemeStateInactiveWindow];
   }
 
   return theme;
 }
 @end