Create NetworkTimeTracker on startup for users in Finch experiment

components/network_time/network_time_tracker.h

 // Copyright 2014 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 COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_
 #define COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_
 
 #include <stdint.h>
 #include <memory>
 
+#include "base/feature_list.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/clock.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "net/url_request/url_fetcher_delegate.h"
 #include "url/gurl.h"
 
@@ skipping 16 matching lines @@
 
 namespace network_time {
 
 // Clock resolution is platform dependent.
 #if defined(OS_WIN)
 const int64_t kTicksResolutionMs = base::Time::kMinLowResolutionThresholdMs;
 #else
 const int64_t kTicksResolutionMs = 1;  // Assume 1ms for non-windows platforms.
 #endif
 
+// Variations Service feature that enables network time service querying.
+extern const base::Feature kNetworkTimeServiceQuerying;
+
 // A class that receives network time updates and can provide the network time
 // for a corresponding local time. This class is not thread safe.
 class NetworkTimeTracker : public net::URLFetcherDelegate {
  public:
   // Describes the result of a GetNetworkTime() call, describing whether
   // network time was available and if not, why not.
   enum NetworkTimeResult {
     // Network time is available.
     NETWORK_TIME_AVAILABLE,
     // A time has been retrieved from the network in the past, but
@@ skipping 113 matching lines @@
   base::TimeDelta network_time_uncertainty_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkTimeTracker);
 };
 
 }  // namespace network_time
 
 #endif  // COMPONENTS_NETWORK_TIME_NETWORK_TIME_TRACKER_H_