Rework service extensions to be safe

runtime/observatory/tests/service/developer_extension_test.dart

Index: runtime/observatory/tests/service/developer_extension_test.dart
diff --git a/runtime/observatory/tests/service/developer_extension_test.dart b/runtime/observatory/tests/service/developer_extension_test.dart
index fcfd66751f8139fe0a97ff585a715a3ef94d70c5..d47a1f6136293484ac6da6522e043cc826b7cee9 100644
--- a/runtime/observatory/tests/service/developer_extension_test.dart
+++ b/runtime/observatory/tests/service/developer_extension_test.dart
@@ -47,6 +47,11 @@ Future<ServiceExtensionResponse> Handler(String method,
   }
 }
 
+Future<ServiceExtensionResponse> LanguageErrorHandler(String method,
+                                                      Map paremeters) {
+   klajsdlkjfad

[Ivan Posva, 2015/08/26 04:46:59]

Please add a comment that you did not just fat-finger here. This is intended,
no?

[Cutch, 2015/08/26 14:28:00]

Done.

+}
+
 void test() {
   registerExtension('__delay', Handler);
   registerExtension('__error', Handler);
@@ -61,6 +66,7 @@ void test() {
     exceptionThrown = true;
   }
   expect(exceptionThrown, isTrue);
+  registerExtension('__languageError', LanguageErrorHandler);
 }
 
 var tests = [
@@ -109,6 +115,16 @@ var tests = [
     expect(result['parameters']['apple'], equals('banana'));
 
 
+    try {
+      result = await isolate.invokeRpcNoUpgrade('__languageError', {});
+    } on ServerRpcException catch (e, st) {
+      expect(e.code, equals(ServiceExtensionResponse.kExtensionError));
+      expect(e.message, stringContainsInOrder([
+          'Error in extension `__languageError`:',
+          'developer_extension_test.dart',
+          'semicolon expected']));
+    }
+
   },
 ];