Add Sync datatype for shared managed user settings.

sync/internal_api/base_node.cc

Index: sync/internal_api/base_node.cc
diff --git a/sync/internal_api/base_node.cc b/sync/internal_api/base_node.cc
index 3f8f2f0aed23243df97d5e55b18c9e0b42aa29e7..e610534f93336c7ddfd5ea57dc6e22bfa0c97d2e 100644
--- a/sync/internal_api/base_node.cc
+++ b/sync/internal_api/base_node.cc
@@ -324,6 +324,12 @@ const sync_pb::ManagedUserSpecifics& BaseNode::GetManagedUserSpecifics() const {
   return GetEntitySpecifics().managed_user();
 }
 
+const sync_pb::ManagedUserSharedSettingSpecifics&
+    BaseNode::GetManagedUserSharedSettingSpecifics() const {
+  DCHECK_EQ(GetModelType(), MANAGED_USER_SHARED_SETTINGS);
+  return GetEntitySpecifics().managed_user_shared_setting();
+}
+
 const sync_pb::DeviceInfoSpecifics& BaseNode::GetDeviceInfoSpecifics() const {
   DCHECK_EQ(GetModelType(), DEVICE_INFO);
   return GetEntitySpecifics().device_info();