Add a Clock and TickClock interface for mocking out time

base/default_clock.h

Index: base/default_clock.h
diff --git a/base/default_clock.h b/base/default_clock.h
new file mode 100644
index 0000000000000000000000000000000000000000..f4b37802ad401f33998f1cec46393ae07b453b9d
--- /dev/null
+++ b/base/default_clock.h
@@ -0,0 +1,29 @@
+// Copyright (c) 2012 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.
+
+#ifndef BASE_DEFAULT_CLOCK_H_
+#define BASE_DEFAULT_CLOCK_H_
+
+#include "base/base_export.h"
+#include "base/clock.h"
+#include "base/compiler_specific.h"
+
+namespace base {
+
+// DefaultClock is a Clock implementation that uses Time::Now().
+class BASE_EXPORT DefaultClock : public Clock {
+ public:
+  virtual ~DefaultClock();
+
+  // Simply returns Time::Now().
+  virtual Time Now() OVERRIDE;
+
+  // Returns a single lazy-initialized instance of DefaultClock.  But
+  // you can create your own DefaultClock object if you wish.
+  static DefaultClock* Get();
+};
+
+}  // namespace base
+
+#endif  // BASE_DEFAULT_CLOCK_H_