MalformedType used for all invalid type annotations.

sdk/lib/_internal/compiler/implementation/universe/universe.dart

Index: sdk/lib/_internal/compiler/implementation/universe/universe.dart
diff --git a/sdk/lib/_internal/compiler/implementation/universe/universe.dart b/sdk/lib/_internal/compiler/implementation/universe/universe.dart
index be913e21c61fe1bff8b83092951b5be8092b9b43..3c6be1821de06d88c78225425113df8ba1d590d2 100644
--- a/sdk/lib/_internal/compiler/implementation/universe/universe.dart
+++ b/sdk/lib/_internal/compiler/implementation/universe/universe.dart
@@ -382,7 +382,10 @@ class TypedSelector extends Selector {
             selector.name,
             selector.library,
             selector.argumentCount,
-            selector.namedArguments);
+            selector.namedArguments) {
+    // Invariant: Typed selector can not be based on a malformed type.
+    assert(!identical(receiverType.kind, TypeKind.MALFORMED_TYPE));
+  }
 
   /**
    * Check if [element] will be the one used at runtime when being