Change gae to apache 2 license.

impl/prod/context_vm.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.
+// 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.
 
 // +build !appengine
 
 package prod
 
 import (
         "golang.org/x/net/context"
         "google.golang.org/appengine"
 )
 
 // UseBackground is the same as Use except that it activates production
 // implementations which aren't associated with any particular request.
 //
 // This is only available on Managed VMs.
 func UseBackground(c context.Context) context.Context {
         return setupAECtx(c, appengine.BackgroundContext())
 }