Add missing AllocateIDs API.

service/datastore/raw_interface.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 (
         "fmt"
 
         "golang.org/x/net/context"
@@ skipping 81 matching lines @@
 // GetSingle gets a single MetaGetter at the specified index.
 func (m MultiMetaGetter) GetSingle(idx int) MetaGetter {
         if idx >= len(m) || m[idx] == nil {
                 return nullMetaGetter
         }
         return m[idx]
 }
 
 // RawInterface implements the datastore functionality without any of the fancy
 // reflection stuff. This is so that Filters can avoid doing lots of redundant
-// reflection work. See datastore.RawInterface for a more user-friendly interface.
+// reflection work. See datastore.Interface for a more user-friendly interface.
 type RawInterface interface {
+        // AllocateIDs allows you to allocate IDs from the datastore without putting
+        // any data. `incomplete` must be a PartialValid Key. If there's no error,
+        // a contiguous block of IDs of n length starting at `start` will be reserved
+        // indefinitely for the user application code for use in new keys. The
+        // appengine automatic ID generator will never automatically assign these IDs
+        // for Keys of this type.
+        AllocateIDs(incomplete *Key, n int) (start int64, err error)
+
         // RunInTransaction runs f in a transaction.
         //
         // opts may be nil.
         //
         // NOTE: Implementations and filters are guaranteed that:
         //   - f is not nil
         RunInTransaction(f func(c context.Context) error, opts *TransactionOptions) error
 
         // DecodeCursor converts a string returned by a Cursor into a Cursor instance.
         // It will return an error if the supplied string is not valid, or could not
@@ skipping 42 matching lines @@
         //   - len(keys) > 0
         //   - all keys are Valid, !Incomplete, and in the current namespace
         //   - none keys of the keys are 'special' (use a kind prefixed with '__')
         //   - cb is not nil
         DeleteMulti(keys []*Key, cb DeleteMultiCB) error
 
         // Testable returns the Testable interface for the implementation, or nil if
         // there is none.
         Testable() Testable
 }