[rename fixit] TwoLevelSublist left->leading, center->title

examples/material_gallery/lib/demo/two_level_list_demo.dart

@@ -15,7 +15,7 @@ class TwoLevelListDemo extends StatelessWidget {
           items: <Widget>[
             new TwoLevelListItem(title: new Text('Top')),
             new TwoLevelSublist(
-              center: new Text('Sublist'),
+              title: new Text('Sublist'),
               children: <Widget>[
                 new TwoLevelListItem(title: new Text('One')),
                 new TwoLevelListItem(title: new Text('Two')),

packages/flutter/lib/src/material/two_level_list.dart

@@ -50,10 +50,10 @@ class TwoLevelListItem extends StatelessWidget {
 }
 
 class TwoLevelSublist extends StatefulWidget {
-  TwoLevelSublist({ Key key, this.left, this.center, this.children }) : super(key: key);
+  TwoLevelSublist({ Key key, this.leading, this.title, this.children }) : super(key: key);
 
-  final Widget left;
-  final Widget center;
+  final Widget leading;
+  final Widget title;
   final List<Widget> children;
 
   _TwoLevelSublistState createState() => new _TwoLevelSublistState();
@@ -108,10 +108,10 @@ class _TwoLevelSublistState extends State<TwoLevelSublist> {
         children: <Widget>[
           new TwoLevelListItem(
             onTap: _handleOnTap,
-            leading: config.left,
+            leading: config.leading,
             title: new DefaultTextStyle(
               style: Theme.of(context).textTheme.subhead.copyWith(color: _headerColor.evaluate(_easeInAnimation)),
-              child: config.center
+              child: config.title
             ),
             trailing: new RotationTransition(
               turns: _iconTurns,

packages/flutter/test/widget/two_level_list_test.dart

@@ -22,7 +22,7 @@ void main() {
                 new TwoLevelListItem(title: new Text('Top'), key: topKey),
                 new TwoLevelSublist(
                   key: sublistKey,
-                  center: new Text('Sublist'),
+                  title: new Text('Sublist'),
                   children: <Widget>[
                     new TwoLevelListItem(title: new Text('0')),
                     new TwoLevelListItem(title: new Text('1'))