Update a suppression (and add a comment) for crbug.com/20504.

chrome/browser/browser_main_mac.mm

 // Copyright (c) 2010 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 "chrome/browser/browser_main_posix.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "app/app_switches.h"
 #include "app/l10n_util_mac.h"
@@ skipping 84 matching lines @@
 
       FilePath resources_pack_path;
       PathService::Get(chrome::FILE_RESOURCES_PACK, &resources_pack_path);
       ResourceBundle::AddDataPackToSharedInstance(resources_pack_path);
     }
 
     // Now load the nib (from the right bundle).
     scoped_nsobject<NSNib>
         nib([[NSNib alloc] initWithNibNamed:@"MainMenu"
                                      bundle:mac_util::MainAppBundle()]);
+    // TODO(viettrungluu): crbug.com/20504 - This currently leaks, so if you
+    // change this, you'll probably need to change the Valgrind suppression.
     [nib instantiateNibWithOwner:NSApp topLevelObjects:nil];
     // Make sure the app controller has been created.
     DCHECK([NSApp delegate]);
 
     // This is a no-op if the KeystoneRegistration framework is not present.
     // The framework is only distributed with branded Google Chrome builds.
     [[KeystoneGlue defaultKeystoneGlue] registerWithKeystone];
 
     // Prevent Cocoa from turning command-line arguments into
     // |-application:openFiles:|, since we already handle them directly.
     [[NSUserDefaults standardUserDefaults]
         setObject:@"NO" forKey:@"NSTreatUnknownArgumentsAsOpen"];
   }
 };
 
 // static
 BrowserMainParts* BrowserMainParts::CreateBrowserMainParts(
     const MainFunctionParams& parameters) {
   return new BrowserMainPartsMac(parameters);
 }