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 aa6891976f43dcf3c4b610b6a68172a6a3a6b6b5..c28e2e631f1b5f9c207b488f07ef157f0e6c0cbd 100644
--- a/lib/compiler/implementation/typechecker.dart
+++ b/lib/compiler/implementation/typechecker.dart
@@ -335,6 +335,7 @@ 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;
@@ -647,7 +648,7 @@ 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;
   }