Effective type can be malformed.

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

Index: pkg/compiler/lib/src/elements/modelx.dart
diff --git a/pkg/compiler/lib/src/elements/modelx.dart b/pkg/compiler/lib/src/elements/modelx.dart
index d2452ef73f6b33ee9b15947918736644bd307143..f3fb7a0223039e5c8ec6bac1d34556c34d9daeff 100644
--- a/pkg/compiler/lib/src/elements/modelx.dart
+++ b/pkg/compiler/lib/src/elements/modelx.dart
@@ -2227,13 +2227,13 @@ abstract class ConstructorElementX extends FunctionElementX
     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);
   }