datastore: Update AllocateIDs to take keys.

service/datastore/raw_interface.go

Index: service/datastore/raw_interface.go
diff --git a/service/datastore/raw_interface.go b/service/datastore/raw_interface.go
index bfb9a9f83da4af42d3427cecc000ca4cdfac4766..ea3b1aad9b5a97861c720027e80feb32eebbfeed 100644
--- a/service/datastore/raw_interface.go
+++ b/service/datastore/raw_interface.go
@@ -105,12 +105,12 @@ func (m MultiMetaGetter) GetSingle(idx int) MetaGetter {
 // 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)
+	// any data. The supplied keys must be PartialValid and share the same entity
+	// type.
+	//
+	// If there's no error, the keys in the slice will be replaced with keys
+	// containing integer IDs assigned to them.
+	AllocateIDs(keys []*Key) error
 
 	// RunInTransaction runs f in a transaction.
 	//