Update dart_backend_test after fixes to optional params.

tests/compiler/dart2js/dart_backend_test.dart

Index: tests/compiler/dart2js/dart_backend_test.dart
diff --git a/tests/compiler/dart2js/dart_backend_test.dart b/tests/compiler/dart2js/dart_backend_test.dart
index 28f2939a3e122b253f94083a6a4d59bcba245b6f..112f0fa5ac02890ca7bf6720e6d67353d23d154d 100644
--- a/tests/compiler/dart2js/dart_backend_test.dart
+++ b/tests/compiler/dart2js/dart_backend_test.dart
@@ -612,7 +612,7 @@ class A {
   }
 }
 
-fooglobal(arg,[optionalarg = 7]) {
+fooglobal(arg,{optionalarg: 7}) {
   arg = 6;
 }
 
@@ -623,7 +623,7 @@ main() {
 }
 ''';
   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);