dart2js: Use js('source') instead of js['source'] to invoke JS mini-parser

tests/compiler/dart2js/js_parser_test.dart

 // Copyright (c) 2011, 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 'mock_compiler.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/js/js.dart' as jsAst;
 import '../../../sdk/lib/_internal/compiler/implementation/js/js.dart' show js;
 
 void testExpression(String expression, [String expect = ""]) {
-  jsAst.Node node = js[expression];
+  jsAst.Node node = js(expression);
   MockCompiler compiler = new MockCompiler();
   String jsText =
       jsAst.prettyPrint(node,
                         compiler,
                         allowVariableMinification: false).getText();
   if (expect == "") {
     Expect.stringEquals(expression, jsText);
   } else {
     Expect.stringEquals(expect, jsText);
   }
 }
 
 void testError(String expression, [String expect = ""]) {
   bool doCheck(exception) {
     Expect.isTrue(exception.toString().contains(expect));
     return true;
   }
-  Expect.throws(() => js[expression], doCheck);
+  Expect.throws(() => js(expression), doCheck);
 }
     
 
 
 void main() {
   // Asterisk indicates deviations from real JS.
   // Simple var test.
   testExpression('var a = ""');
   // Parse and print will normalize whitespace.
   testExpression(' var  a  =  "" ', 'var a = ""');
@@ skipping 108 matching lines @@
   testExpression("y = a == null ? b : a");
   testExpression("y = a == null ? b + c : a + c");
   testExpression("foo = a ? b : c ? d : e");
   testExpression("foo = a ? b ? c : d : e");
   testExpression("foo = (a = v) ? b = w : c = x ? d = y : e = z");
   testExpression("foo = (a = v) ? b = w ? c = x : d = y : e = z");
   // Stacked assignment.
   testExpression("a = b = c");
   testExpression("var a = b = c");
 }