Add Sync datatype for shared managed user settings.

sync/protocol/managed_user_shared_setting_specifics.proto

 // Copyright (c) 2013 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.
 //
-// Sync protocol datatype extension for managed user settings.
+// Sync protocol datatype extension for managed user shared settings.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 option retain_unknown_fields = true;
 
 package sync_pb;
 
-// Properties of managed user setting sync objects.
-message ManagedUserSettingSpecifics {
-  optional string name = 1;
-  optional string value = 2;
+// Properties of managed user shared setting sync objects.
+message ManagedUserSharedSettingSpecifics {
+  optional string mu_id = 1;

[Denis Kuznetsov (DE-MUC), 2013/11/26 10:42:30]

I believe that this protobuf should act more like Manager's one (have specific
fields, rather than key-value pairs): most of the values need to change at once,
transactionally, e.g. password and version of the password.
In addition, we need similar acknowledgment flag (or, better, version) to make
sure it is safe to apply password changes on device.

[Bernhard Bauer, 2013/11/26 11:05:46]

Well, transaction semantics are exactly what you don't get with the optimistic
concurrency model of Sync. What if the user decides to change their avatar while
the manager changes the password for that user?

Also, this way we can add additional fields without having to change the Sync
protobuf.
I think we'll be able to retire the acknowledgement flag for the MANAGED_USER
datatype once we get synchronous out-of-band user creation. If you want to have
a password version, just make that an additional shared setting.

+  optional string key = 2;
+  optional string value = 3;
 }