Add a mojo interface for AccountId

components/signin/core/account_id/account_id.h

 // 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.
 
 #ifndef COMPONENTS_SIGNIN_CORE_ACCOUNT_ID_ACCOUNT_ID_H_
 #define COMPONENTS_SIGNIN_CORE_ACCOUNT_ID_ACCOUNT_ID_H_
 
 #include <stddef.h>
 
 #include <string>
 #include "base/containers/hash_tables.h"
 
 enum class AccountType { UNKNOWN, GOOGLE, ACTIVE_DIRECTORY };
 
 // Type that contains enough information to identify user.
 //
 // TODO(alemate): we are in the process of moving away from std::string as a
 // type for storing user identifier to AccountId. At this time GaiaId is mostly
 // empty, so this type is used as a replacement for e-mail string.
 // But in near future AccountId will become full feature user identifier.
 // TODO(alemate): Rename functions and fields to reflect different types of
 // accounts. (see crbug.com/672253)
 class AccountId {
  public:
   struct EmptyAccountId;
 
+  AccountId();

[msarda, 2017/01/09 10:28:50]

Why is this change needed?

[xiyuan, 2017/01/09 17:42:57]

This is needed for mojo deserialization. The code needs to create an AccoundId
instance using default ctor and pass it as output pointer to StructTraits::Read.

Think the original intention to make the default ctor private is to force using
one of the static FromXXXX method to construct an AccountId. This move does not
change that. The default ctor creates an invalid/emtpy AccountId (is_valid()
returns false for such instance). So any caller still has to fill it up with
proper data.

We probably can get rid of EmptyAccountId now after this move since the public
default ctor would provide the same capability. If you want, I can create a
follow up CL to get rid of that.

[msarda, 2017/01/10 15:04:22]

Thank you for the explanation. I am fine with us adding this constructor - I
think having the empty account id is also interesting in the log run.

May I ask you to add a comment about this constructor like:
// Creates an empty account id.
//
// Note: This constructor is public as it is required for mojo
// serialization. To create an AccountId object, prefer using the
// static FromXXXX methods or the EmptyAccountId method when
// creating an empty account id.

[xiyuan, 2017/01/12 00:06:54]

Done.

   AccountId(const AccountId& other);
 
   // If any of the comparable AccountIds has AccountType == UNKNOWN then it
   // compares emails.
   // If both are not UNKNOWN and not equal then it returns false.
   // If AccountType == GOOGLE then it checks if either ids or emails are equal.
   // If AccountType == ACTIVE_DIRECTORY then it checks if ids and emails are
   // equal.
   bool operator==(const AccountId& other) const;
   bool operator!=(const AccountId& other) const;
@@ skipping 46 matching lines @@
 
   // These are (for now) unstable and cannot be used to store serialized data to
   // persistent storage. Only in-memory storage is safe.
   // Serialize() returns JSON dictionary,
   // Deserialize() restores AccountId after serialization.
   std::string Serialize() const;
   static bool Deserialize(const std::string& serialized,
                           AccountId* out_account_id);
 
  private:
-  AccountId();
   AccountId(const std::string& id,
             const std::string& user_email,
             const AccountType& account_type);
 
   std::string id_;
   std::string user_email_;
   AccountType account_type_ = AccountType::UNKNOWN;
 };
 
 // Returns a reference to a singleton.
 const AccountId& EmptyAccountId();
 
 namespace BASE_HASH_NAMESPACE {
 
 // Implement hashing of AccountId, so it can be used as a key in STL containers.
 template <>
 struct hash<AccountId> {
   std::size_t operator()(const AccountId& user_id) const;
 };
 
 }  // namespace BASE_HASH_NAMESPACE
 
 #endif  // COMPONENTS_SIGNIN_CORE_ACCOUNT_ID_ACCOUNT_ID_H_