A method or accessor with empty body is implicitly abstract.

dart/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.
 
 part of tree;
 
 abstract class Visitor<R> {
   const Visitor();
 
   abstract R visitNode(Node node);
@@ skipping 617 matching lines @@
 
   visitChildren(Visitor visitor) {
     if (modifiers != null) modifiers.accept(visitor);
     if (returnType != null) returnType.accept(visitor);
     if (name != null) name.accept(visitor);
     if (parameters != null) parameters.accept(visitor);
     if (initializers != null) initializers.accept(visitor);
     if (body != null) body.accept(visitor);
   }
 
-  bool hasBody() {
-    // TODO(karlklose,ahe): refactor AST nodes (issue 1713).
-    if (body.asReturn() != null) return true;
-    NodeList statements = body.asBlock().statements;
-    return (!statements.nodes.isEmpty ||
-            !identical(statements.getBeginToken().kind, $SEMICOLON));
+  bool hasBody() => body.asEmptyStatement() == null;
+
+  bool hasEmptyBody() {
+    Block block = body.asBlock();
+    if (block == null) return false;
+    return block.statements.isEmpty;
   }
 
   Token getBeginToken() {
     Token token = firstBeginToken(modifiers, returnType);
     if (token != null) return token;
     if (getOrSet != null) return getOrSet;
     return firstBeginToken(name, parameters);
   }
 
   Token getEndToken() {
@@ skipping 1341 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);
 }