Handle deferred access of unserialized code.

pkg/compiler/lib/src/serialization/modelz.dart

 // Copyright (c) 2015, 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.
 
 /// Implementation of the element model used for deserialiation.
 ///
 /// These classes are created by [ElementDeserializer] triggered by the
 /// [Deserializer].
 
 library dart2js.serialization.modelz;
@@ skipping 464 matching lines @@
   }
 
   @override
   void forEachImport(f(Element element)) {
     _ensureImports();
     _importsMap.forEach(f);
   }
 
   @override
   Iterable<ImportElement> getImportsFor(Element element) {
-    return _unsupported('getImportsFor');
+    // TODO(johnniwinther): Serialize this to support deferred access to
+    // serialized entities.
+    return <ImportElement>[];
   }
 
   String toString() {
     return 'Zlibrary(${canonicalUri})';
   }
 
   @override
   Iterable<ExportElement> get exports {
     if (_exports == null) {
       _exports = _decoder.getElements(Key.EXPORTS, isOptional: true);
@@ skipping 831 matching lines @@
   }
 
   @override
   PrefixElement get redirectionDeferredPrefix {
     _ensureRedirection();
     return _redirectionDeferredPrefix;
   }
 }
 
 class ForwardingConstructorElementZ extends ElementZ
-    with AnalyzableElementMixin, AstElementMixinZ
-    implements ConstructorElement {
+    with
+        AnalyzableElementMixin,
+        AstElementMixinZ
+    implements
+        ConstructorElement,
+        // TODO(johnniwinther): Sort out whether a constructor is a method.
+        MethodElement {
   final MixinApplicationElement enclosingClass;
   final ConstructorElement definingConstructor;
 
   ForwardingConstructorElementZ(this.enclosingClass, this.definingConstructor);
 
   @override
   CompilationUnitElement get compilationUnit => enclosingClass.compilationUnit;
 
   @override
   accept(ElementVisitor visitor, arg) {
@@ skipping 897 matching lines @@
   }
 
   @override
   ElementKind get kind => ElementKind.PREFIX;
 
   @override
   Element lookupLocalMember(String memberName) {
     return _unsupported('lookupLocalMember');
   }
 }