MalformedType used for all invalid type annotations.

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index d73707ac72cd69bb1be6e6a79f8121699a28b269..035f7c9adb27c357285c151b2500732f09f981a9 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -1095,6 +1095,8 @@ class JavaScriptBackend extends Backend {
           : const SourceString('stringSuperTypeCheck');
     } else if (identical(element, compiler.listClass)) {
       return const SourceString('listTypeCheck');
+    } else if (type.isMalformed) {
+      return const SourceString('malformedTypeCheck');
     } else {
       if (Elements.isListSupertype(element, compiler)) {
         return nativeCheck