Use {To/From}JavaTime for policy timestamps

components/policy/core/common/cloud/cloud_policy_client.cc

Index: components/policy/core/common/cloud/cloud_policy_client.cc
diff --git a/components/policy/core/common/cloud/cloud_policy_client.cc b/components/policy/core/common/cloud/cloud_policy_client.cc
index fff57a08c12422e059ee6701913d7660120285e2..a6e24817137bdb3bf8f4a76ce049877d6de72d6a 100644
--- a/components/policy/core/common/cloud/cloud_policy_client.cc
+++ b/components/policy/core/common/cloud/cloud_policy_client.cc
@@ -237,11 +237,8 @@ void CloudPolicyClient::FetchPolicy() {
     if (IsChromePolicy(type_to_fetch.first)) {
       if (submit_machine_id_ && !machine_id_.empty())
         fetch_request->set_machine_id(machine_id_);
-      if (!last_policy_timestamp_.is_null()) {
-        base::TimeDelta timestamp(
-            last_policy_timestamp_ - base::Time::UnixEpoch());
-        fetch_request->set_timestamp(timestamp.InMilliseconds());
-      }
+      if (!last_policy_timestamp_.is_null())
+        fetch_request->set_timestamp(last_policy_timestamp_.ToJavaTime());
       if (!invalidation_payload_.empty()) {
         fetch_request->set_invalidation_version(invalidation_version_);
         fetch_request->set_invalidation_payload(invalidation_payload_);