[current results ui] Clear input field after entering filter term

Change-Id: Ibc6c76ead653c9e7714687d3e7bb6ee59f527b6c
Reviewed-on: https://dart-review.googlesource.com/c/dart_ci/+/161981
Reviewed-by: Alexander Thomas <athom@google.com>
diff --git a/current_results_ui/lib/filter.dart b/current_results_ui/lib/filter.dart
index 755800f..43f3a04 100644
--- a/current_results_ui/lib/filter.dart
+++ b/current_results_ui/lib/filter.dart
@@ -47,18 +47,35 @@
   }
 }
 
-class AddWidget extends StatelessWidget {
+class AddWidget extends StatefulWidget {
   final Filter filter;
   AddWidget(this.filter);
 
   @override
+  _AddWidgetState createState() => _AddWidgetState();
+}
+
+class _AddWidgetState extends State<AddWidget> {
+  final controller = TextEditingController();
+
+  @override
+  void dispose() {
+    controller.dispose();
+    super.dispose();
+  }
+
+  @override
   Widget build(BuildContext context) {
     return SizedBox(
       width: 200.0,
       height: 40.0,
       child: TextField(
+        controller: controller,
         decoration: InputDecoration(hintText: 'Test or configuration prefix'),
-        onSubmitted: (value) => filter.addAll(value),
+        onSubmitted: (value) {
+          widget.filter.addAll(value);
+          controller.text = '';
+        },
       ),
     );
   }