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 63c21ae1d96038be034e5c151fbb096d2f641c82..a566b0f42434941147d8aa240c8bc6625e968a11 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -1105,6 +1105,8 @@ 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