Fix static type warnings in test.dart.

tools/testing/dart/test_options.dart

Index: tools/testing/dart/test_options.dart
diff --git a/tools/testing/dart/test_options.dart b/tools/testing/dart/test_options.dart
index 0d6e72104c2ba26b03e0ae059a0104ef2aabc10f..79ebb2d978e83c710d71e3ed8a6747a1d13d36a1 100644
--- a/tools/testing/dart/test_options.dart
+++ b/tools/testing/dart/test_options.dart
@@ -406,11 +406,11 @@ is 'dart file.dart' and you specify special command
         var buffer = new StringBuffer();;
         buffer.add(name);
         if (option.type == 'bool') {
-          assert(option.values.empty());
+          assert(option.values.isEmpty());
         } else {
           buffer.add(name.startsWith('--') ? '=' : ' ');
           if (option.type == 'int') {
-            assert(option.values.empty());
+            assert(option.values.isEmpty());
             buffer.add('n (default: ${option.defaultValue})');
           } else {
             buffer.add('[');