Fix analyzer warnings in service tests

runtime/observatory/tests/service/gc_test.dart

Index: runtime/observatory/tests/service/gc_test.dart
diff --git a/runtime/observatory/tests/service/gc_test.dart b/runtime/observatory/tests/service/gc_test.dart
index 49e653ea9921e1da527a5c33e55ff77e9c95d584..e5adaedf7a262f9854a1b610a5c8bc57b9ca6226 100644
--- a/runtime/observatory/tests/service/gc_test.dart
+++ b/runtime/observatory/tests/service/gc_test.dart
@@ -9,13 +9,12 @@ import 'test_helper.dart';
 import 'dart:async';
 
 void script() {
-  List<int> data;
   var grow;
   grow = (int iterations, int size, Duration duration) {
     if (iterations <= 0) {
       return;
     }
-    data = new List<int>(size);
+    new List<int>(size);
     new Timer(duration, () => grow(iterations - 1, size, duration));
   };
   grow(100, 1 << 24, new Duration(seconds: 1));