[Mac] Workaround for Mavericks AppKit accessibility bug in NSCollectionView.

ui/app_list/cocoa/apps_grid_view_item.mm

 // Copyright 2013 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 "ui/app_list/cocoa/apps_grid_view_item.h"
 
 #include "base/mac/foundation_util.h"
 #include "base/mac/mac_util.h"
 #include "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
@@ skipping 440 matching lines @@
   [shadow setShadowBlurRadius:2.0];
   [shadow setShadowColor:[NSColor colorWithCalibratedWhite:0
                                                      alpha:0.14]];
   [shadow set];
 
   [super drawImage:image
          withFrame:frame
             inView:controlView];
 }
 
+// Workaround for http://crbug.com/324365: AppKit in Mavericks tries to call
+// - [NSButtonCell item] when inspecting accessibility. Without this, an
+// unrecognized selector exception is thrown inside AppKit, crashing Chrome.
+- (id)item {
+  return nil;
+}
+
 @end