Add erroneous elements for function types and use them to allow unresolvable constructors to be han…

lib/compiler/implementation/typechecker.dart

Index: lib/compiler/implementation/typechecker.dart
diff --git a/lib/compiler/implementation/typechecker.dart b/lib/compiler/implementation/typechecker.dart
index 8c36f1f797c130ca126d8835e49d6f1753b77471..a5489eedaaff9abb5f814cad83d1e11d1d80fb65 100644
--- a/lib/compiler/implementation/typechecker.dart
+++ b/lib/compiler/implementation/typechecker.dart
@@ -395,6 +395,7 @@ class TypeCheckerVisitor implements Visitor<Type> {
     Type returnType;
     Type previousType;
     final FunctionElement element = elements[node];
+    if (Element.isInvalid(element)) return types.dynamicType;
     if (element.kind === ElementKind.GENERATIVE_CONSTRUCTOR ||
         element.kind === ElementKind.GENERATIVE_CONSTRUCTOR_BODY) {
       type = types.dynamicType;
@@ -707,7 +708,7 @@ class TypeCheckerVisitor implements Visitor<Type> {
   }
 
   Type computeType(Element element) {
-    if (element === null) return types.dynamicType;
+    if (Element.isInvalid(element)) return types.dynamicType;
     Type result = element.computeType(compiler);
     return (result !== null) ? result : types.dynamicType;
   }