Add better error reporting to utils tests.

tests/utils/dummy_compiler_test.dart

Index: tests/utils/dummy_compiler_test.dart
diff --git a/tests/utils/dummy_compiler_test.dart b/tests/utils/dummy_compiler_test.dart
index 2405b7753bf6523befd4824ed8d59ec06a7a7ae9..2e858f0287f498f0dc923ad58c23f83ba2584502 100644
--- a/tests/utils/dummy_compiler_test.dart
+++ b/tests/utils/dummy_compiler_test.dart
@@ -61,7 +61,7 @@ main() {
     if (code == null) {
       throw 'Compilation failed';
     }
-  }, onError: (e) {
-      throw 'Compilation failed: $e';
+  }, onError: (e, s) {
+      throw 'Compilation failed: $e\n$s';
   }).then(asyncSuccess);
 }