Add a missing comment to a switch I recently added.

chrome/common/chrome_switches.cc

 // 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/common/chrome_switches.h"
 
 #include "base/base_switches.h"
 #include "base/command_line.h"
 
 namespace switches {
@@ skipping 41 matching lines @@
 const char kAppId[]                         = "app-id";
 
 // Specifying this flag allows the webstorePrivate APIs to return browser (aka
 // sync) login tokens to be used for auto-login in the Web Store (normally they
 // do not).
 const char kAppsGalleryReturnTokens[]       = "apps-gallery-return-tokens";
 
 // The URL to use for the gallery link in the app launcher.
 const char kAppsGalleryURL[]                = "apps-gallery-url";
 
+// The update url used by gallery/webstore extensions.
 const char kAppsGalleryUpdateURL[]          = "apps-gallery-update-url";
 
 // Disable throbber for extension apps.
 const char kAppsNoThrob[]                   = "apps-no-throb";
 
 // Whitelist of servers that Negotiate will generate delegated Kerberos tickets
 // for.
 const char kAuthNegotiateDelegateWhitelist[] =
     "auth-negotiate-delegate-whitelist";
 
@@ skipping 1288 matching lines @@
 
 // -----------------------------------------------------------------------------
 // DO NOT ADD YOUR CRAP TO THE BOTTOM OF THIS FILE.
 //
 // You were going to just dump your switches here, weren't you? Instead,
 // please put them in alphabetical order above, or in order inside the
 // appropriate ifdef at the bottom. The order should match the header.
 // -----------------------------------------------------------------------------
 
 }  // namespace switches