Add Info Testable interface, implement for memory.

service/info/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 info
 
 import (
         "time"
 
         "golang.org/x/net/context"
@@ skipping 18 matching lines @@
         ServerSoftware() string
         ServiceAccount() (string, error)
         VersionID() string
 
         Namespace(namespace string) (context.Context, error)
         MustNamespace(namespace string) context.Context
 
         AccessToken(scopes ...string) (token string, expiry time.Time, err error)
         PublicCertificates() ([]Certificate, error)
         SignBytes(bytes []byte) (keyName string, signature []byte, err error)
+
+        // Testable returns this Interface's Testable interface. Testing will return
+        // nil if testing is not supported in this implementation.
+        Testable() Testable
 }
+
+// Testable is an additional set of functions for testing instrumentation.
+type Testable interface {
+        SetVersionID(string) context.Context
+        SetRequestID(string) context.Context
+}