Fix a bug in the Kernel testing framework

pkg/kernel/test/baseline_tester.dart

Index: pkg/kernel/test/baseline_tester.dart
diff --git a/pkg/kernel/test/baseline_tester.dart b/pkg/kernel/test/baseline_tester.dart
index b71870a02d6cc31f17c71f82a5777111a3706401..e79251b4d3898f38f20abf33a07ee458ba0bf508 100644
--- a/pkg/kernel/test/baseline_tester.dart
+++ b/pkg/kernel/test/baseline_tester.dart
@@ -54,7 +54,8 @@ void runBaselineTests(String folderName, TestTarget target) {
                 applicationRoot: applicationRoot));
         var program = loader.loadProgram(dartPath, target: target);
         verifyProgram(program);
-        var errors = target.performModularTransformations(program);
+        var errors = <String>[];
+        errors.addAll(target.performModularTransformations(program));
         verifyProgram(program);
         errors.addAll(target.performGlobalTransformations(program));
         verifyProgram(program);