Seems like this is all that is required to support callable JS objects. dartbug.com/25321

BUG=
R=sra@google.com

Review URL: https://codereview.chromium.org/2164483004 .

Author: jacob314

pkg/compiler/lib/src/diagnostics/messages.dart

@@ -3703,11 +3703,6 @@ Your app imports dart:mirrors via:"""
           """
 $MIRRORS_NOT_SUPPORTED_BY_BACKEND_PADDING#{importChain}"""),
 
-      MessageKind.CALL_NOT_SUPPORTED_ON_NATIVE_CLASS: const MessageTemplate(
-          MessageKind.CALL_NOT_SUPPORTED_ON_NATIVE_CLASS,
-          "Non-supported 'call' member on a native class, or a "
-          "subclass of a native class."),
-
       MessageKind.DIRECTLY_THROWING_NSM: const MessageTemplate(
           MessageKind.DIRECTLY_THROWING_NSM,
           "This 'noSuchMethod' implementation is guaranteed to throw an "

pkg/compiler/lib/src/js_backend/backend.dart

@@ -945,8 +945,6 @@ class JavaScriptBackend extends Backend {
       cls.ensureResolved(resolution);
       cls.forEachMember((ClassElement classElement, Element member) {
         if (member.name == Identifiers.call) {
-          reporter.reportErrorMessage(
-              member, MessageKind.CALL_NOT_SUPPORTED_ON_NATIVE_CLASS);
           return;
         }
         if (member.isSynthesized) return;

tests/html/html.status

@@ -358,6 +358,7 @@ js_interop_1_test: SkipByDesign
 js_test: SkipByDesign
 js_array_test: SkipByDesign
 js_typed_interop_bind_this_test: SkipByDesign
+js_typed_interop_callable_object_test: SkipByDesign
 js_typed_interop_test: SkipByDesign
 js_typed_interop_default_arg_test: SkipByDesign
 js_typed_interop_type_test: SkipByDesign

tests/html/js_typed_interop_callable_object_test.dart

@@ -0,0 +1,72 @@
+// Copyright (c) 2016, 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.
+
+@JS()
+library js_typed_interop_callable_object_test;
+
+import 'dart:html';
+
+import 'package:expect/expect.dart' show NoInline, AssumeDynamic;
+import 'package:js/js.dart';
+import 'package:unittest/html_config.dart';
+import 'package:unittest/html_individual_config.dart';
+import 'package:unittest/unittest.dart';
+
+// This is a regression test for https://github.com/dart-lang/sdk/issues/25658
+
+@NoInline()
+@AssumeDynamic()
+confuse(x) => x;
+
+_injectJs() {
+  document.body.append(new ScriptElement()
+    ..type = 'text/javascript'
+    ..innerHtml = r"""
+  "use strict";
+
+  window.callableObject = function (a, b) { return a + b; };
+  window.callableObject.foo = function() { return "bar"; };
+  window.callableObject.bar = 42;
+
+""");
+}
+
+@JS()
+@anonymous
+class CallableObject {
+  /// If a @JS class implements `call`, the underlying representation must be
+  /// a JavaScript callable (i.e. function).
+  external num call(num a, num b);
+  external int get bar;
+  external String foo();
+}
+
+@JS()
+external CallableObject get callableObject;
+
+main() {
+  _injectJs();
+
+  useHtmlIndividualConfiguration();
+
+  group('callable object', () {
+    test('simple', () {
+      var obj = callableObject;
+      expect(obj(4, 5), equals(9));
+      expect(obj.bar, equals(42));
+      expect(obj.foo(), equals("bar"));
+
+      expect(callableObject(4, 5), equals(9));
+      expect(callableObject.bar, equals(42));
+      expect(callableObject.foo(), equals("bar"));
+    });
+
+    test('dynamic', () {
+      var obj = confuse(callableObject);
+      expect(obj(4, 5), equals(9));
+      expect(obj.bar, equals(42));
+      expect(obj.foo(), equals("bar"));
+    });
+  });
+}