Support the new isolate load error messages.

test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart

Index: test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart
diff --git a/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart b/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart
index f2c6e6adc635ead361a5acb8c9d949c2ec9d224d..2a307228dada14992da606f9c160e794c793c728 100644
--- a/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart
+++ b/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart
@@ -28,8 +28,7 @@ main() {
     pubGet();
     var pub = startPubServe();
     pub.stderr.expect("Unable to spawn isolate: Unhandled exception:");
-    pub.stderr.expect(
-        startsWith("Load Error for "));
+    pub.stderr.expect(startsWith('Could not import "'));
     pub.shouldExit(1);
   });
 }