[Extensions UI] Handle multiple warning bubbles racing to show

chrome/browser/ui/cocoa/extensions/toolbar_actions_bar_bubble_mac.mm

 // 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.
 
 #import "chrome/browser/ui/cocoa/extensions/toolbar_actions_bar_bubble_mac.h"
 
 #include <utility>
 
 #include "base/mac/foundation_util.h"
 #include "base/strings/sys_string_conversions.h"
@@ skipping 99 matching lines @@
 }
 
 // Private /////////////////////////////////////////////////////////////////////
 
 - (void)windowWillClose:(NSNotification*)notification {
   if (!acknowledged_) {
     delegate_->OnBubbleClosed(
         ToolbarActionsBarBubbleDelegate::CLOSE_DISMISS_DEACTIVATION);
     acknowledged_ = YES;
   }
+  // Deallocation happens asynchronously in Cocoa, but that makes testing
+  // difficult. Explicitly destroy |delegate_| here so it can perform any
+  // necessary cleanup.
+  delegate_.reset();
   [super windowWillClose:notification];
 }
 
 - (NSAttributedString*)attributedStringWithString:(const base::string16&)string
                                          fontSize:(CGFloat)fontSize
                                         alignment:(NSTextAlignment)alignment {
   NSString* cocoaString = base::SysUTF16ToNSString(string);
   base::scoped_nsobject<NSMutableParagraphStyle> paragraphStyle(
       [[NSMutableParagraphStyle alloc] init]);
   [paragraphStyle setAlignment:alignment];
@@ skipping 209 matching lines @@
   } else {
     DCHECK_EQ(sender, actionButton_);
     action = ToolbarActionsBarBubbleDelegate::CLOSE_EXECUTE;
   }
   acknowledged_ = YES;
   delegate_->OnBubbleClosed(action);
   [self close];
 }
 
 @end