Decouple PLS from MGS.

service/datastore/properties.go

 // 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.
 
 package datastore
 
 import (
         "encoding/base64"
         "errors"
         "fmt"
@@ skipping 662 matching lines @@
         // error occurs, it's returned via error. If non-fatal conversion errors
         // occur, error will be a MultiError containing one or more ErrFieldMismatch
         // objects.
         Load(PropertyMap) error
 
         // Save returns the current property as a PropertyMap. if withMeta is true,
         // then the PropertyMap contains all the metadata (e.g. '$meta' fields)
         // which was held by this PropertyLoadSaver.
         Save(withMeta bool) (PropertyMap, error)
 
-        MetaGetterSetter
-
         // Problem indicates that this PLS has a fatal problem. Usually this is
         // set when the underlying struct has recursion, invalid field types, nested
         // slices, etc.
         Problem() error
 }
 
 // MetaGetterSetter is the subset of PropertyLoadSaver which pertains to
 // getting and saving metadata.
 //
 // A *struct may implement this interface to provide metadata which is
@@ skipping 148 matching lines @@
         dflt = UpconvertUnderlyingType(dflt)
         cur, err := gm(key)
         if err != nil {
                 return dflt
         }
         if dflt != nil && reflect.TypeOf(cur) != reflect.TypeOf(dflt) {
                 return dflt
         }
         return cur
 }