Handle use of constant constructors with default values.

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

Index: pkg/compiler/lib/src/serialization/modelz.dart
diff --git a/pkg/compiler/lib/src/serialization/modelz.dart b/pkg/compiler/lib/src/serialization/modelz.dart
index 3c10292cf4e2079c6d044f9dc1d819f0af9b7bb2..f721eb17d400258bff929f4cc35f82eb832f9cb1 100644
--- a/pkg/compiler/lib/src/serialization/modelz.dart
+++ b/pkg/compiler/lib/src/serialization/modelz.dart
@@ -1108,6 +1108,9 @@ abstract class ConstructorElementZ extends DeserializedElementZ
   ConstructorElement get definingConstructor => null;
 
   @override
+  bool get hasEffectiveTarget => true;
+
+  @override
   ConstructorElement get effectiveTarget {
     if (_effectiveTarget == null) {
       _effectiveTarget =
@@ -1256,7 +1259,7 @@ class ForwardingConstructorElementZ extends ElementZ
 
   @override
   InterfaceType computeEffectiveTargetType(InterfaceType newType) {
-    return enclosingClass.thisType;
+    return enclosingClass.thisType.substByContext(newType);
   }
 
   @override
@@ -1269,6 +1272,9 @@ class ForwardingConstructorElementZ extends ElementZ
   ConstantConstructor get constantConstructor => null;
 
   @override
+  bool get hasEffectiveTarget => true;
+
+  @override
   ConstructorElement get effectiveTarget => this;
 
   @override
@@ -1405,6 +1411,9 @@ abstract class FieldElementZ extends DeserializedElementZ
   }
 
   @override
+  bool get hasConstant => true;
+
+  @override
   ConstantExpression get constant {
     _ensureConstant();
     return _constant;
@@ -1852,6 +1861,9 @@ abstract class ParameterElementZ extends DeserializedElementZ
   bool get isConst => false;
 
   @override
+  bool get hasConstant => true;
+
+  @override
   ConstantExpression get constant {
     if (isOptional) {
       if (_constant == null) {
@@ -1980,6 +1992,9 @@ class LocalVariableElementZ extends DeserializedElementZ
   }
 
   @override
+  bool get hasConstant => true;
+
+  @override
   ConstantExpression get constant {
     if (isConst) {
       return _constant;