Merge pull request #146 from dart-lang/late_finals

mark fields `late final`

Author: pq

lib/src/usage_impl.dart

@@ -75,7 +75,7 @@ class AnalyticsImpl implements Analytics {
   @override
   AnalyticsOpt analyticsOpt = AnalyticsOpt.optOut;
 
-  late String _url;
+  late final String _url;
 
   final StreamController<Map<String, dynamic>> _sendController =
       StreamController.broadcast(sync: true);

lib/src/usage_impl_html.dart

@@ -59,7 +59,7 @@ class HtmlPostHandler extends PostHandler {
 }
 
 class HtmlPersistentProperties extends PersistentProperties {
-  late Map _map;
+  late final Map _map;
 
   HtmlPersistentProperties(String name) : super(name) {
     var str = window.localStorage[name];

lib/src/usage_impl_io.dart

@@ -108,7 +108,7 @@ class IOPostHandler extends PostHandler {
 JsonEncoder _jsonEncoder = JsonEncoder.withIndent('  ');
 
 class IOPersistentProperties extends PersistentProperties {
-  late File _file;
+  late final File _file;
   late Map _map;
 
   IOPersistentProperties(String name, {String? documentDirPath}) : super(name) {

lib/usage.dart

@@ -160,7 +160,7 @@ class AnalyticsTimer {
   final String? category;
   final String? label;
 
-  late int _startMillis;
+  late final int _startMillis;
   int? _endMillis;
 
   AnalyticsTimer(this.analytics, this.variableName,