Fix a couple of bugs in handling of factory redirections.

dart/sdk/lib/_internal/compiler/implementation/ssa/builder.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 ssa;
 
 class Interceptors {
   Compiler compiler;
   Interceptors(Compiler this.compiler);
 
@@ skipping 3127 matching lines @@
     // TODO(5347): Try to avoid the need for calling [implementation] before
     // calling [addStaticSendArgumentsToList].
     bool succeeded = addStaticSendArgumentsToList(selector, node.arguments,
                                                   constructor.implementation,
                                                   inputs);
     if (!succeeded) {
       generateWrongArgumentCountError(node, constructor, node.arguments);
       return;
     }
 
-    if (type.element.modifiers.isAbstract() &&
+    if (constructor.getEnclosingClass().isAbstract(compiler) &&
         constructor.isGenerativeConstructor()) {
       generateAbstractClassInstantiationError(node, type.name.slowToString());
       return;
     }
     if (compiler.world.needsRti(constructor.enclosingElement)) {
       if (!type.arguments.isEmpty) {
         type.arguments.forEach((DartType argument) {
           inputs.add(analyzeTypeArgument(argument, node));
         });
       } else if (compiler.enabledRuntimeType) {
@@ skipping 1669 matching lines @@
           new HSubGraphBlockInformation(elseBranch.graph));
 
     HBasicBlock conditionStartBlock = conditionBranch.block;
     conditionStartBlock.setBlockFlow(info, joinBlock);
     SubGraph conditionGraph = conditionBranch.graph;
     HIf branch = conditionGraph.end.last;
     assert(branch is HIf);
     branch.blockInformation = conditionStartBlock.blockFlow;
   }
 }