Retain abstract classes.

dart/sdk/lib/_internal/compiler/implementation/enqueue.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 dart2js;
 
 class EnqueueTask extends CompilerTask {
   final ResolutionEnqueuer resolution;
   final CodegenEnqueuer codegen;
 
@@ skipping 308 matching lines @@
   void pretendElementWasUsed(Element element, TreeElements elements) {
     if (Elements.isUnresolved(element)) {
       // Ignore.
     } else if (element.isSynthesized
                && element.getLibrary().isPlatformLibrary) {
       // TODO(ahe): Work-around for http://dartbug.com/11205.
     } else if (element.isConstructor()) {
       ClassElement cls = element.declaration.getEnclosingClass();
       registerInstantiatedType(cls.rawType, elements);
       registerStaticUse(element.declaration);
+    } else if (element.isMixinApplication) {
+      // Don't enqueue mixin applications.
+    } else if (element.isClass()) {
+      ClassElement cls = element.declaration;
+      registerInstantiatedType(cls.rawType, elements);
+      // Make sure that even abstract classes are considered instantiated.
+      universe.instantiatedClasses.add(cls);
     } else if (element.impliesType()) {
-      // Don't enqueue classes, typedefs, and type variables.
+      // Don't enqueue typedefs, and type variables.
     } else if (Elements.isStaticOrTopLevel(element)) {
       registerStaticUse(element.declaration);
     } else if (element.isInstanceMember()) {
       Selector selector = new Selector.fromElement(element, compiler);
       registerSelectorUse(selector);
       if (element.isField()) {
         Selector selector =
             new Selector.setter(element.name, element.getLibrary());
         registerInvokedSetter(selector);
       }
@@ skipping 381 matching lines @@
     while(!queue.isEmpty) {
       // TODO(johnniwinther): Find an optimal process order for codegen.
       f(queue.removeLast());
     }
   }
 
   void _logSpecificSummary(log(message)) {
     log('Compiled ${generatedCode.length} methods.');
   }
 }