fix handling of malformed typedefs

pkg/compiler/lib/src/dart_types.dart

Index: pkg/compiler/lib/src/dart_types.dart
diff --git a/pkg/compiler/lib/src/dart_types.dart b/pkg/compiler/lib/src/dart_types.dart
index fb0eac4b9c7c844a32e05832f11294b4cb8abbc5..6efca512b8fd8c67b7f7c32232debc613a49e842 100644
--- a/pkg/compiler/lib/src/dart_types.dart
+++ b/pkg/compiler/lib/src/dart_types.dart
@@ -845,6 +845,10 @@ class TypedefType extends GenericType {
   void computeUnaliased(Resolution resolution) {
     if (_unaliased == null) {
       element.ensureResolved(resolution);
+      if (element.isMalformed) {
+        _unaliased = const DynamicType();
+        return;
+      }
       element.checkCyclicReference(resolution);
       element.alias.computeUnaliased(resolution);
       _unaliased = element.alias.unaliased.substByContext(this);