Correctly skip if-null expressions.

pkg/compiler/lib/src/parser/partial_parser.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 dart2js.parser.partial;
 
 import '../common.dart';
 import '../options.dart' show ParserOptions;
 import '../util/characters.dart' as Characters show $CLOSE_CURLY_BRACKET;
 import '../tokens/token.dart' show BeginGroupToken, ErrorToken, Token;
@@ skipping 31 matching lines @@
       if ((identical(kind, Tokens.EOF_TOKEN)) ||
           (identical(value, ';')) ||
           (identical(value, ',')) ||
           (identical(value, '}')) ||
           (identical(value, ')')) ||
           (identical(value, ']'))) {
         break;
       }
       if (identical(value, '=') ||
           identical(value, '?') ||
-          identical(value, ':')) {
+          identical(value, ':') ||
+          identical(value, '??')) {
         var nextValue = token.next.stringValue;
         if (identical(nextValue, 'const')) {
           token = token.next;
           nextValue = token.next.stringValue;
         }
         if (identical(nextValue, '{')) {
           // Handle cases like this:
           // class Foo {
           //   var map;
           //   Foo() : map = {};
@@ skipping 104 matching lines @@
         return token;
       }
       return listener.unexpected(token);
     }
     BeginGroupToken beginGroupToken = token;
     Token endToken = beginGroupToken.endGroup;
     listener.endFormalParameters(0, token, endToken);
     return endToken.next;
   }
 }