Use the right command for dartc.

tools/testing/dart/test_config_utils.dart

Index: tools/testing/dart/test_config_utils.dart
diff --git a/tools/testing/dart/test_config_utils.dart b/tools/testing/dart/test_config_utils.dart
index 50219b104217013f4f271ef015d170a263d30d38..9e54863de32df99a2f10d55302678552e26f9010 100644
--- a/tools/testing/dart/test_config_utils.dart
+++ b/tools/testing/dart/test_config_utils.dart
@@ -23,6 +23,11 @@ class TestUtils {
     if (configuration["component"] == "leg") {
       args.add("--enable_leg");
     }
+    if (configuration["component"] == "dartc") {
+      if (configuration["mode"] == "release") {
+        args.add("--optimize");
+      }
+    }
 
     List<String> dartOptions = optionsFromFile["dartOptions"];
     args.addAll(dartOptions == null ? [filename] : dartOptions);