Update dart_backend_test after fixes to optional params.

tests/compiler/dart2js/dart_backend_test.dart

 // Copyright (c) 2012, 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:async';
 import 'parser_helper.dart';
 import 'mock_compiler.dart';
 import '../../../sdk/lib/_internal/compiler/compiler.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart' as leg;
@@ skipping 594 matching lines @@
 testParametersMinified() {
   var src = '''
 class A {
   var a;
   static foo(arg1) {
     // Should not rename arg1 to a.
     arg1 = 5;
   }
 }
 
-fooglobal(arg,[optionalarg = 7]) {
+fooglobal(arg,{optionalarg: 7}) {
   arg = 6;
 }
 
 main() {
   new A().a;
   A.foo(8);
   fooglobal(8);
 }
 ''';
   var expectedResult =
-      'class B{var E;static C(A){A=5;}}D(A,[optionalarg=7]){A=6;}'
+      'class B{var E;static C(A){A=5;}}D(A,{optionalarg: 7}){A=6;}'
       'main(){new B().E;B.C(8);D(8);}';
   testDart2Dart(src, continuation:
       (String result) { Expect.equals(expectedResult, result); }, minify: true);
 }
 
 testDeclarationTypePlaceholders() {
   var src = '''
 String globalfield;
 const String globalconstfield;
 
@@ skipping 86 matching lines @@
   testStaticAccessIoLib();
   testLocalFunctionPlaceholder();
   testMinification();
   testClosureLocalsMinified();
   testParametersMinified();
   testDeclarationTypePlaceholders();
   testPlatformLibraryMemberNamesAreFixed();
   testConflictsWithCoreLib();
   testUnresolvedNamedConstructor();
 }