Add context-aware "time" library wrapper.

go/src/infra/libs/clock/timer.go

+// Copyright (c) 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 clock
+
+import (
+        "time"
+)
+
+// Timer is a wrapper around the time.Timer structure.
+type Timer interface {
+        GetC() <-chan time.Time     // Returns the underlying timer's channel, or nil if not configured.
+        Reset(d time.Duration) bool // See time.Timer.
+        Stop() bool                 // See time.Timer.
+}
+
+//
+// systemTimer
+//
+
+// A Timer implementation that uses time.Timer.
+type systemTimer struct {
+        T *time.Timer // The underlying timer. Starts as nil, is initialized on Reset.
+}
+
+// Implements Timer.
+func (t *systemTimer) GetC() (c <-chan time.Time) {
+        if t.T != nil {
+                c = t.T.C
+        }
+        return
+}
+
+// Implements Timer.
+func (t *systemTimer) Reset(d time.Duration) bool {
+        if t.T == nil {
+                t.T = time.NewTimer(d)
+                return false
+        }
+        return t.T.Reset(d)
+}
+
+// Implements Timer.
+func (t *systemTimer) Stop() bool {
+        if t.T == nil {
+                return false
+        }
+        return t.T.Stop()
+}