Use a stable device-user identifier for CryptAuth enrollments.

components/proximity_auth/cryptauth/cryptauth_enrollment_utils.cc

+// Copyright 2015 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 "components/proximity_auth/cryptauth/cryptauth_enrollment_utils.h"
+
+#include "base/sha1.h"
+#include "components/proximity_auth/base64url.h"
+
+namespace proximity_auth {
+
+std::string CalculateDeviceUserId(const std::string& device_id,
+                                  const std::string& user_id) {
+  std::string device_user_id;
+  Base64UrlEncode(base::SHA1HashString(device_id + "|" + user_id),
+                  &device_user_id);
+  return device_user_id;
+}
+
+}  // namespace proximity_auth