Add a mojo interface for AccountId

components/signin/public/interfaces/account_id_traits.h

Index: components/signin/public/interfaces/account_id_traits.h
diff --git a/components/signin/public/interfaces/account_id_traits.h b/components/signin/public/interfaces/account_id_traits.h
new file mode 100644
index 0000000000000000000000000000000000000000..5360345d71e6dc71a56a0126056155f4d6557e19
--- /dev/null
+++ b/components/signin/public/interfaces/account_id_traits.h
@@ -0,0 +1,34 @@
+// 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.
+
+#ifndef COMPONENTS_SIGNIN_PUBLIC_INTERFACES_ACCOUNT_ID_TRAITS_H_
+#define COMPONENTS_SIGNIN_PUBLIC_INTERFACES_ACCOUNT_ID_TRAITS_H_
+
+#include <string>
+
+#include "components/signin/core/account_id/account_id.h"
+#include "components/signin/public/interfaces/account_id.mojom.h"
+
+namespace mojo {
+
+template <>
+struct StructTraits<signin::mojom::AccountIdDataView, AccountId> {
+  static std::string serialized(const AccountId& r) {
+    return r.Serialize();
+  }
+  static bool Read(signin::mojom::AccountIdDataView data, AccountId* out) {
+    std::string serialized;
+    if (!data.ReadSerialized(&serialized))
+      return false;
+
+    if (!AccountId::Deserialize(serialized, out))

[Tom Sepez, 2017/01/05 23:53:28]

Is this ever called on the browser side or in another privileged context?  If
so, it has to be bullet-proof, and right now this is using the base JSON parser,
which we generally don't trust.  I thought there was a safe JSON package that
shipped this off to a utility process.  Can we use that here?

[xiyuan, 2017/01/06 00:22:47]

This runs in browser and (ash process in mash). Currently we are passing
serialized account id as a string and call AccountId::Deserialize to translate
that back to an AccountId. This CL wraps up that logic into typemapping and
should not make it less safe. What is the main concern? Some one would inject
data into a mojo channel and cause us to crash? If that is the case, how could
passing a string or a SkBitmap through mojo is safe?

Not sure safe JSON is good to use here because of its asynchronous nature. The
parsed value is obtained via a callback and I don't know whether we should hold
the Read function to wait for the callback.

[xiyuan, 2017/01/06 16:41:57]

Let me change signin.mojom.AccountId to a similar struct of real AccountId. This
way we could rely on mojo's serialization and avoid the unsafe JSON parser.

+      return false;
+
+    return out->is_valid();
+  }
+};
+
+}  // namespace mojo
+
+#endif  // COMPONENTS_SIGNIN_PUBLIC_INTERFACES_ACCOUNT_ID_TRAITS_H_