Compute ConstructorElement.returnType/type dynamically.

pkg/analyzer/lib/src/dart/element/element.dart

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index 7c1e056917cbf7af237cbf95e6229ffb651e92c1..0e62f2391d83a023947777444115f7e606ef1592 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -1085,7 +1085,6 @@ class ClassElementImpl extends AbstractClassElementImpl
           new ConstructorElementImpl(superclassConstructor.name, -1);
       implicitConstructor.synthetic = true;
       implicitConstructor.redirectedConstructor = superclassConstructor;
-      implicitConstructor.returnType = type;
       List<ParameterElement> superParameters = superclassConstructor.parameters;
       int count = superParameters.length;
       if (count > 0) {
@@ -1106,7 +1105,6 @@ class ClassElementImpl extends AbstractClassElementImpl
         implicitConstructor.parameters = implicitParameters;
       }
       implicitConstructor.enclosingElement = this;
-      implicitConstructor.type = new FunctionTypeImpl(implicitConstructor);
       return implicitConstructor;
     }).toList(growable: false);
   }
@@ -1882,6 +1880,19 @@ class ConstructorElementImpl extends ExecutableElementImpl
   @override
   DartType get returnType => enclosingElement.type;
 
+  void set returnType(DartType returnType) {
+    assert(false);
+  }
+
+  @override
+  FunctionType get type {
+    return _type ??= new FunctionTypeImpl(this);
+  }
+
+  void set type(FunctionType type) {
+    assert(false);
+  }
+
   @override
   accept(ElementVisitor visitor) => visitor.visitConstructorElement(this);