Store a network's last connected timestamp in the sync proto.

Bug: 966270
Change-Id: If3e181f61e0cbf3dd5adb673c182797ee6a42006
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2097835Reviewed-by: Azeem Arshad <azeemarshad@chromium.org>
Reviewed-by: James Vecore <vecore@google.com>
Commit-Queue: Jon Mann <jonmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749769}

chromeos/components/sync_wifi/local_network_collector_impl.cc

@@ -149,6 +149,9 @@ void LocalNetworkCollectorImpl::StartGetNetworkDetails(
   proto.set_hex_ssid(network->type_state->get_wifi()->hex_ssid);
   proto.set_security_type(
       SecurityTypeProtoFromMojo(network->type_state->get_wifi()->security));
+  base::TimeDelta timestamp =
+      network_metadata_store_->GetLastConnectedTimestamp(network->guid);
+  proto.set_last_update_timestamp(timestamp.InMilliseconds());
   cros_network_config_->GetManagedProperties(
       network->guid,
       base::BindOnce(&LocalNetworkCollectorImpl::OnGetManagedPropertiesResult,

chromeos/components/sync_wifi/local_network_collector_impl_unittest.cc

@@ -77,13 +77,15 @@ class LocalNetworkCollectorImplTest : public testing::Test {
   }
 
   void OnGetSyncableNetwork(
-      std::string expected,
+      std::string expected_ssid,
       base::Optional<sync_pb::WifiConfigurationSpecifics> result) {
-    if (expected.empty()) {
+    if (expected_ssid.empty()) {
       ASSERT_EQ(base::nullopt, result);
       return;
     }
-    EXPECT_EQ(expected, DecodeHexString(result->hex_ssid()));
+    EXPECT_EQ(expected_ssid, DecodeHexString(result->hex_ssid()));
+    EXPECT_TRUE(result->has_last_update_timestamp());
+    EXPECT_NE(0, result->last_update_timestamp());
   }
 
   LocalNetworkCollector* local_network_collector() {