Use a stable device-user identifier for CryptAuth enrollments.

chrome/common/extensions/api/easy_unlock_private.idl

 // Copyright 2014 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.
 
 // <code>chrome.easyUnlockPrivate</code> API that provides hooks to Chrome to
 // be used by Easy Unlock component app.
 namespace easyUnlockPrivate {
   // Signature algorithms supported by the crypto library methods used by
   // Easy Unlock.
   enum SignatureType {
@@ skipping 126 matching lines @@
 
     // Websafe base64 encoded persistent symmetric key.
     DOMString? psk;
   };
 
   // The information about a user associated with Easy unlock service.
   dictionary UserInfo {
     // The user id.
     DOMString userId;
 
+    // A stable identifier for the user and device. If a user is removed and
+    // added to the same device, this id will remain the same. However, this id
+    // will be different if another user is added to the same device or if the
+    // same user is added on another device.
+    DOMString deviceUserId;
+
     // Whether the user is logged in. If not logged in, the app is running on
     // the signin screen.
     boolean loggedIn;
 
     // Whether to require the remote device to be in very close proximity before
     // allowing unlock (~1 feet).
     boolean requireCloseProximity;
 
     // Whether all data needed to use Easy unlock service has been loaded for
     // the user.
@@ skipping 224 matching lines @@
     // Event fired when the data for the user currently associated with
     // Easy unlock service is updated.
     // |userInfo| The updated user information.
     static void onUserInfoUpdated(UserInfo userInfo);
 
     // Event fired at the end of Easy bootstrap to start auto pairing so
     // that a proper cryptohome key could be generated for the user.
     static void onStartAutoPairing();
   };
 };