Deferred (aka lazy) loading of static functions.

dart/sdk/lib/_internal/compiler/implementation/elements/elements.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.
 
 library elements;
 
 import 'dart:uri';
 
 import 'modelx.dart';
 import '../tree/tree.dart';
@@ skipping 757 matching lines @@
 
 abstract class TypeVariableElement extends Element {
   TypeVariableType get type;
   DartType get bound;
 
   // TODO(kasperl): Try to get rid of these.
   void set type(TypeVariableType value);
   void set bound(DartType value);
 }
 
-abstract class MetadataAnnotation {
+abstract class MetadataAnnotation implements Spannable {
   Constant get value;
   Element get annotatedElement;
   int get resolutionState;
   Token get beginToken;
 
   // TODO(kasperl): Try to get rid of these.
   void set annotatedElement(Element value);
   void set resolutionState(int value);
 
   MetadataAnnotation ensureResolved(Compiler compiler);
 }