Support runtime check of function types.

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

Index: sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
index cd4e627f8b9f9e0ec02109d88fd2d231417dc98d..e8c613a3fa55b4bc5628fa89b99c3ba51d0235c3 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
@@ -15,7 +15,17 @@ import 'dart:_foreign_helper' show DART_CLOSURE_TO_JS,
                                    JS_OBJECT_CLASS_NAME,
                                    JS_OPERATOR_AS_PREFIX,
                                    JS_OPERATOR_IS_PREFIX,
-                                   RAW_DART_FUNCTION_REF;
+                                   JS_SETUP_OBJECT,
+                                   JS_SIGNATURE_NAME,
+                                   JS_HAS_EQUALS,
+                                   JS_FUNCTION_TYPE_TAG,
+                                   JS_FUNCTION_TYPE_VOID_RETURN_TAG,
+                                   JS_FUNCTION_TYPE_RETURN_TYPE_TAG,
+                                   JS_FUNCTION_TYPE_REQUIRED_PARAMETERS_TAG,
+                                   JS_FUNCTION_TYPE_OPTIONAL_PARAMETERS_TAG,
+                                   JS_FUNCTION_TYPE_NAMED_PARAMETERS_TAG,
+                                   RAW_DART_FUNCTION_REF,
+                                   UNINTERCEPTED;
 import 'dart:_interceptors';
 import "dart:_collection-dev" as _symbol_dev;
 
@@ -186,7 +196,7 @@ class Primitives {
     JS('void', 'throw "Unable to print message: " + String(#)', string);
   }
 
-  static void _throwFormatException(String string) {
+  static _throwFormatException(String string) {
     throw new FormatException(string);
   }