Change core lib, dart2js, and more for new optional parameters syntax

utils/pub/yaml/model.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.
 
 // This file contains the node classes for the internal representations of YAML
 // documents. These nodes are used for both the serialization tree and the
 // representation graph.
 
 /** A tag that indicates the type of a YAML node. */
 class _Tag {
@@ skipping 100 matching lines @@
   final value;
 
   /**
    * Creates a new Scalar node.
    *
    * Exactly one of [content] and [value] should be specified. Content should be
    * specified for a newly-parsed scalar that hasn't yet been composed. Value
    * should be specified for a composed scalar, although `null` is a valid
    * value.
    */
-  _ScalarNode(String tagName, [String content, this.value])
+  _ScalarNode(String tagName, {String content, this.value})
    : _content = content,
      super(new _Tag.scalar(tagName));
 
   /** Two scalars are equal if their string representations are equal. */
   bool operator ==(other) {
     // Should be super != other; bug 2554
     if (!(super == other) || other is! _ScalarNode) return false;
     return content == other.content;
   }
 
@@ skipping 97 matching lines @@
   String toString() {
     var strContent = Strings.join(content.getKeys().
         map((k) => '${k}: ${content[k]}'), ', ');
     return '$tag {$strContent}';
   }
 
   int hashCode() => super.hashCode() ^ _hashCode(content);
 
   visit(_Visitor v) => v.visitMapping(this);
 }