Report arity errors on user definable operators.

sdk/lib/_internal/compiler/implementation/dart2jslib.dart

Index: sdk/lib/_internal/compiler/implementation/dart2jslib.dart
diff --git a/sdk/lib/_internal/compiler/implementation/dart2jslib.dart b/sdk/lib/_internal/compiler/implementation/dart2jslib.dart
index 2d75159ef0028e681668d89965880124910e3957..dc6e1f27ab948a89a68db0425f5ae18c441897e0 100644
--- a/sdk/lib/_internal/compiler/implementation/dart2jslib.dart
+++ b/sdk/lib/_internal/compiler/implementation/dart2jslib.dart
@@ -27,7 +27,12 @@ import 'resolution/resolution.dart';
 import 'js/js.dart' as js;
 
 export 'resolution/resolution.dart' show TreeElements, TreeElementMapping;
-export 'scanner/scannerlib.dart' show SourceString, isUserDefinableOperator;
+export 'scanner/scannerlib.dart' show SourceString,
+                                      isUserDefinableOperator,
+                                      isUnaryOperator,
+                                      isBinaryOperator,
+                                      isTernaryOperator,
+                                      isMinusOperator;
 export 'universe/universe.dart' show Selector;
 
 part 'code_buffer.dart';