Mac File Dialogs: Add Apple radar id in comment about crash.

ui/shell_dialogs/select_file_dialog_mac.mm

 // Copyright (c) 2012 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 "ui/shell_dialogs/select_file_dialog_mac.h"
 
 #include <CoreServices/CoreServices.h>
 #include <stddef.h>
 
 #include <vector>
@@ skipping 293 matching lines @@
     [popup addItemWithTitle:type_description];
 
     // Populate file_type_lists.
     // Set to store different extensions in the current extension group.
     NSMutableSet* file_type_set = [NSMutableSet set];
     for (const base::FilePath::StringType& ext : ext_list) {
       if (ext == default_extension)
         default_extension_index = i;
 
       // Crash reports suggest that CreateUTIFromExtension may return nil. Hence
-      // we nil check before adding to |file_type_set|. See crbug.com/630101.
+      // we nil check before adding to |file_type_set|. See crbug.com/630101 and
+      // rdar://27490414.
       base::ScopedCFTypeRef<CFStringRef> uti(CreateUTIFromExtension(ext));
       if (uti)
         [file_type_set addObject:base::mac::CFToNSCast(uti.get())];
 
       // Always allow the extension itself, in case the UTI doesn't map
       // back to the original extension correctly. This occurs with dynamic
       // UTIs on 10.7 and 10.8.
       // See http://crbug.com/148840, http://openradar.me/12316273
       base::ScopedCFTypeRef<CFStringRef> ext_cf(
           base::SysUTF8ToCFStringRef(ext));
@@ skipping 120 matching lines @@
     // For save dialogs, this causes the first item in the allowedFileTypes
     // array to be used as the extension for the save panel.
     [dialog_ setAllowedFileTypes:[fileTypeLists_ objectAtIndex:index]];
   } else {
     // The user selected "All files" option.
     [dialog_ setAllowedFileTypes:nil];
   }
 }
 
 @end