[Sync] Add full history sync experiment

chrome/browser/sync/profile_sync_service.cc

Index: chrome/browser/sync/profile_sync_service.cc
diff --git a/chrome/browser/sync/profile_sync_service.cc b/chrome/browser/sync/profile_sync_service.cc
index b16c3728ac29f826c984ac740774012002bd26fa..ca82c69896e3965e62c92c2cb788ff2270f5017b 100644
--- a/chrome/browser/sync/profile_sync_service.cc
+++ b/chrome/browser/sync/profile_sync_service.cc
@@ -931,6 +931,12 @@ void ProfileSyncService::OnExperimentsChanged(
                                       true);
   }
 
+  if (experiments.full_history_sync) {
+    about_flags::SetExperimentEnabled(g_browser_process->local_state(),
+                                      syncer::kFullHistorySyncFlag,
+                                      true);
+  }
+
   current_experiments_ = experiments;
 }