Effective type can be malformed.

pkg/compiler/lib/src/elements/modelx.dart

 // Copyright (c) 2013, 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.modelx;
 
 import '../common.dart';
 import '../common/resolution.dart' show Resolution, Parsing;
 import '../compiler.dart' show Compiler;
 import '../constants/constant_constructors.dart';
@@ skipping 2209 matching lines @@
     assert(!isRedirectingFactory || effectiveTargetInternal != null);
     if (isRedirectingFactory) {
       return effectiveTargetInternal;
     }
     if (isPatched) {
       return effectiveTargetInternal ?? this;
     }
     return this;
   }
 
-  InterfaceType get effectiveTargetType {
+  DartType get effectiveTargetType {
     assert(invariant(this, _effectiveTargetType != null,
         message: 'Effective target type has not yet been computed for $this.'));
     return _effectiveTargetType;
   }
 
-  InterfaceType computeEffectiveTargetType(InterfaceType newType) {
+  DartType computeEffectiveTargetType(InterfaceType newType) {
     if (!isRedirectingFactory) return newType;
     return effectiveTargetType.substByContext(newType);
   }
 
   bool get isEffectiveTargetMalformed {
     if (!isRedirectingFactory) return false;
     assert(invariant(this, _isEffectiveTargetMalformed != null,
         message: 'Malformedness has not yet been computed for $this.'));
     return _isEffectiveTargetMalformed == true;
   }
@@ skipping 880 matching lines @@
 
   bool get hasResolvedAst {
     return definingElement.hasNode && definingElement.hasTreeElements;
   }
 
   ResolvedAst get resolvedAst {
     return new ResolvedAst(
         declaration, definingElement.node, definingElement.treeElements);
   }
 }