Give access to a network time kept in the variation service.

chrome/browser/metrics/variations/network_time_tracker.h

Index: chrome/browser/metrics/variations/network_time_tracker.h
diff --git a/chrome/browser/metrics/variations/network_time_tracker.h b/chrome/browser/metrics/variations/network_time_tracker.h
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+++ b/chrome/browser/metrics/variations/network_time_tracker.h
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+// Copyright (c) 2013 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 CHROME_BROWSER_METRICS_VARIATIONS_NETWORK_TIME_TRACKER_H_
+#define CHROME_BROWSER_METRICS_VARIATIONS_NETWORK_TIME_TRACKER_H_
+
+#include "base/time.h"
+
+// A class that tracks time based on a provided network time, using system's
+// tick time to properly offset it, and also provide uncertainty.
+class NetworkTimeTracker {
+ public:
+  NetworkTimeTracker();
+  virtual ~NetworkTimeTracker();
+
+  // Returns a network time based on values provided to UpdateNetworkTime and
+  // CPU ticks count since then. Returns false if no network time is available
+  // yet. Can also return the error range if |uncertainty| isn't NULL.
+  bool GetNetworkTime(base::Time* network_time,
+                      base::TimeDelta* uncertainty) const;
+
+  // The provided |network_time| is precise at the given |resolution| and
+  // represent the time between now and up to |latency| ago.
+  void UpdateNetworkTime(const base::Time& network_time,
+                         const base::TimeDelta& resolution,
+                         const base::TimeDelta& latency);
+ protected:
+  // Used for a derviced test class to mock the current CPU ticks time.
+  virtual base::TimeTicks GetTicksNow() const;
+
+ private:
+  // Returns true in NDEBUG, and validate time tracking when NDEBUG isn't
+  // defined, returning FALSE if the network time has drifted too far.
+  bool ValidateTimeTracking(const base::Time& new_network_time,
+                            const base::TimeDelta& resolution,
+                            const base::TimeDelta& latency);
+
+  // Remember the network time based on last call to UpdateNetworkTime().
+  base::Time network_time_;
+
+  // The estimated ticks count when |network_time_| was set based on the
+  // system's tick count.
+  base::TimeTicks network_time_ticks_;
+
+  // Uncertainty of |network_time_| based on added inaccuracies/resolution.
+  base::TimeDelta network_time_uncertainty_;
+
+  DISALLOW_COPY_AND_ASSIGN(NetworkTimeTracker);
+};
+
+#endif  // CHROME_BROWSER_METRICS_VARIATIONS_NETWORK_TIME_TRACKER_H_