Fix behavior when typed JS interop getters are called as functions.

tests/html/js_function_getter_trust_types_test.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// SharedOptions=--trust-type-annotations
+@JS()
+library js_function_getter_trust_types_test;
+
+import 'dart:html';
+
+import 'package:js/js.dart';
+import 'package:unittest/unittest.dart';
+import 'package:unittest/html_config.dart';
+import 'package:unittest/html_individual_config.dart';
+
+_injectJs() {
+  document.body.append(new ScriptElement()
+    ..type = 'text/javascript'
+    ..innerHtml = r"""
+  var bar = { };
+
+  bar.nonFunctionStatic = function() {
+    return arguments.length * 2;
+  };
+
+  bar.add = function(a, b) {
+    return a + b;
+  };
+
+  var foo = { 'bar' : bar };
+""");
+}
+
+typedef int AddFn(int x, int y);
+
+@JS()
+class NotAFn { }
+
+@JS()
+abstract class Bar {
+  external AddFn get add;
+  external NotAFn get nonFunctionStatic;
+}
+
+@JS()
+abstract class Foo {
+  external Bar get bar;
+}
+
+@JS()
+external Foo get foo;
+
+main() {
+  _injectJs();
+
+  useHtmlIndividualConfiguration();
+
+  group('trust types', () {
+    test('static nonFunctionStatic', () {
+      expect(() => foo.bar.nonFunctionStatic(), throws);
+      expect(() => foo.bar.nonFunctionStatic(0), throws);
+      expect(() => foo.bar.nonFunctionStatic(0,0), throws);
+      expect(() => foo.bar.nonFunctionStatic(0,0,0,0,0,0), throws);
+    });
+
+    test('typedef function', () {
+      expect(() => foo.bar.add(4), throws);
+      expect(() => foo.bar.add(4,5,10), throws);
+      expect(foo.bar.add(4,5), equals(9));
+    });
+  });
+}