Uncomment and clean up engine_test.dart

pkg/analyzer/lib/src/generated/java_core.dart

Index: pkg/analyzer/lib/src/generated/java_core.dart
diff --git a/pkg/analyzer/lib/src/generated/java_core.dart b/pkg/analyzer/lib/src/generated/java_core.dart
index 48afe1f79fadeb00101c3ced05e8a8a76c3f0cf5..16cfe12b8fb255885cfa074140f0355bd4e735db 100644
--- a/pkg/analyzer/lib/src/generated/java_core.dart
+++ b/pkg/analyzer/lib/src/generated/java_core.dart
@@ -335,15 +335,22 @@ class NumberFormatException extends JavaException {
 
 /// Parses given string to [Uri], throws [URISyntaxException] if invalid.
 Uri parseUriWithException(String str) {
-  Uri uri = Uri.parse(str);
+  Uri uri;
+  try {
+    uri = Uri.parse(str);
+  } on FormatException catch (e) {
+    throw new URISyntaxException(e.toString());
+  }
   if (uri.path.isEmpty) {
-    throw new URISyntaxException();
+    throw new URISyntaxException('empty path');
   }
   return uri;
 }
 
 class URISyntaxException implements Exception {
-  String toString() => "URISyntaxException";
+  final String message;
+  URISyntaxException(this.message);
+  String toString() => "URISyntaxException: $message";
 }
 
 class MissingFormatArgumentException implements Exception {