Add a mojo interface for AccountId

components/signin/public/interfaces/account_id.mojom

Index: components/signin/public/interfaces/account_id.mojom
diff --git a/components/signin/public/interfaces/account_id.mojom b/components/signin/public/interfaces/account_id.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..f0f9abdc1a3db7a4f8e4da777e7f6191a591385c
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+++ b/components/signin/public/interfaces/account_id.mojom
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+// Copyright 2017 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.
+
+module signin.mojom;
+
+// Matches AccountType of AccountId.
+enum AccountType {
+  UNKNOWN,
+  GOOGLE,
+  ACTIVE_DIRECTORY,
+};
+
+// Mirror of AccountId in Mojo.
+struct AccountId {
+  AccountType account_type;
+  string id;
+  string user_email;
+};