Fix accessing private members on extension classes.

Since the member was already a symbol, canonicalMember() was incorrectly
double wrapping it.

Fixes #508.

[email protected]

Review URL: https://codereview.chromium.org/1944293003 .

Author: munificent

pkg/dev_compiler/lib/runtime/dart_sdk.js

@@ -239,6 +239,7 @@ dart_library.library('dart_sdk', null, /* Imports */[
     });
   };
   dart.canonicalMember = function(obj, name) {
+    if (typeof name === 'symbol') return name;
     if (obj != null && obj[dart._extensionType]) return dart.dartx[name];
     if (name == 'constructor' || name == 'prototype') {
       name = '+' + name;

pkg/dev_compiler/test/codegen/lib/html/private_extension_member_test.dart

@@ -0,0 +1,18 @@
+// 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.
+
+import 'package:expect/expect.dart';
+
+import 'dart:html';
+
+main() {
+  // Regression test for: https://github.com/dart-lang/dev_compiler/issues/508.
+  // "dart:html" defines some private members on native DOM types and we need
+  // to ensure those can be accessed correctly.
+  //
+  // The createFragment() method sets `_innerHtml` on the element, so we use it
+  // as a test case.
+  Expect.equals("[object DocumentFragment]",
+      new BRElement().createFragment("Hi").toString());
+}

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/classes.dart

@@ -343,6 +343,9 @@ defineExtensionMembers(type, methodNames) => JS('', '''(() => {
 })()''');
 
 canonicalMember(obj, name) => JS('', '''(() => {
+  // Private names are symbols and are already canonical.
+  if (typeof name === 'symbol') return name;
+
   if ($obj != null && $obj[$_extensionType]) return $dartx[$name];
   // Check for certain names that we can't use in JS
   if ($name == 'constructor' || $name == 'prototype') {