Fix prefix variable parse errors

tests/language/src/library12.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.
 //
 
 #library("library12.dart");
 
 #import("library11.dart");
 class Library12 {
   Library12(this.fld);
+  Library12.other(fld, multiplier) {
+    this.fld = fld*multiplier;
+  }
   func() {
     return 2;
   }
   var fld;
   static static_func() {
     var result = 0;
     var obj = new Library11(4);
     result = obj.fld;
     Expect.equals(4, result);
     result += obj.func();
@@ skipping 10 matching lines @@
 }
 
 interface Library12Interface {
   Library12 addObjects(Library12 value1, Library12 value2);
 }
 
 final int top_level12 = 10;
 top_level_func12() {
   return 20;
 }