Add Context cancellation to clock.

common/gcloud/pubsub/subscriber/subscriber.go

 // Copyright 2016 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 subscriber
 
 import (
         "sync"
         "time"
 
@@ skipping 146 matching lines @@
 // sleep. This is a simple method to obtain the desired effect of avoiding
 // pointless burst Pub/Sub spam when the service has nothing useful to offer.
 func (s *Subscriber) noDataSleep(c context.Context) {
         s.noDataMu.Lock()
         defer s.noDataMu.Unlock()
 
         d := s.NoDataDelay
         if d <= 0 {
                 d = DefaultNoDataDelay
         }
-        cancellableSleep(c, d)
+        clock.CancelSleep(c, d)
 }
-
-// cancellableSleep sleeps, returning either when the sleep duration has expired
-// or the supplied context has been canceled.
-func cancellableSleep(c context.Context, delay time.Duration) {
-        // Sleep for "delay", stopping early if our Context is canceled.
-        select {
-        case <-clock.After(c, delay):
-                break
-
-        case <-c.Done():
-                break
-        }
-}