Create NetworkTimeTracker on startup for users in Finch experiment

components/network_time/network_time_tracker.h

Index: components/network_time/network_time_tracker.h
diff --git a/components/network_time/network_time_tracker.h b/components/network_time/network_time_tracker.h
index 5e06fa6e58b0743b8b9a3710b3a030658a098554..32a51e6acb78dfecf00389aed67702a51c6bd02c 100644
--- a/components/network_time/network_time_tracker.h
+++ b/components/network_time/network_time_tracker.h
@@ -8,6 +8,7 @@
 #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"
@@ -44,6 +45,9 @@ const int64_t kTicksResolutionMs = base::Time::kMinLowResolutionThresholdMs;
 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 {