Minor fixes to remove some warnings.

lib/compiler/implementation/tree/nodes.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.
 
 interface Visitor<R> {
   R visitBlock(Block node);
   R visitBreakStatement(BreakStatement node);
   R visitCascade(Cascade node);
   R visitCascadeReceiver(CascadeReceiver node);
   R visitCatchBlock(CatchBlock node);
@@ skipping 1357 matching lines @@
 
   Link<Token> caseKeywords() {
     Token token = startToken;
     if (label !== null) {
       // Skip past the label: <Identifier> ':'.
       token = token.next.next;
     }
     LinkBuilder<Token> builder = new LinkBuilder<Token>();
     Link<Expression> link = expressions.nodes;
     while (token.stringValue === 'case') {
-      assert(token.next === link.head.getBeginToken(0));
+      assert(token.next === link.head.getBeginToken());
       builder.addLast(token);
       Token colon = link.head.getEndToken().next;
       token = colon.next;
       link = link.tail;
     }
     return builder.toLink();
   }
 }
 
 class GotoStatement extends Statement {
@@ skipping 292 matching lines @@
  * argument).
  *
  * TODO(ahe): This method is controversial, the team needs to discuss
  * if top-level methods are acceptable and what naming conventions to
  * use.
  */
 initializerDo(Node node, f(Node node)) {
   SendSet send = node.asSendSet();
   if (send !== null) return f(send.arguments.head);
 }