Interface update, per-method Contexts.

service/datastore/raw_interface.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package datastore
 
 import (
         "fmt"
 
         "golang.org/x/net/context"
@@ skipping 166 matching lines @@
         // receives an error, it will immediately forward that error and stop
         // subsequent callbacks.
         //
         // NOTE: Implementations and filters are guaranteed that
         //   - 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
+        // WithTransaction, given a Context, returns a derived Context with the
+        // supplied datastore Transaction installed.
+        WithTransaction(Transaction) context.Context
+
+        // CurrentTransaction returns a reference to the current Transaction, or nil
+        // if the Context does not have a current Transaction.
+        CurrentTransaction() Transaction
+
+        // GetTestable returns the Testable interface for the implementation, or nil
+        // if there is none.
+        GetTestable() Testable
 }