tools/test.dart: Implement --checked option.

tests/corelib/test_config.dart

Index: tests/corelib/test_config.dart
diff --git a/tests/corelib/test_config.dart b/tests/corelib/test_config.dart
index 4932cb25ecfe5001bb6ee6b1fc064e0c40f4406c..9bb4c09479d3e459b7fa84348d89cf5c4648b1a7 100644
--- a/tests/corelib/test_config.dart
+++ b/tests/corelib/test_config.dart
@@ -54,12 +54,15 @@ class CorelibTestSuite {
     //               until they are handled correctly.
     if (expectations.contains(SKIP)) return;
 
+    List args = ["--ignore-unrecognized-flags"];
+    if (configuration["checked"]) {
+      args.add("--enable-type-checks");
+    }
+    args.add(filename);
 
     doTest(new TestCase(testName,
                         shellPath,
-                        <String>["--enable_type_checks",
-                                 "--ignore-unrecognized-flags",
-                                 filename ],
+                        args,
                         completeHandler,
                         expectations));
   }