Don't crash on deserialized type inference.

pkg/compiler/lib/src/js_backend/backend.dart

Index: pkg/compiler/lib/src/js_backend/backend.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend.dart b/pkg/compiler/lib/src/js_backend/backend.dart
index 1e964430fe44fdb66637c0fae98c43499826248f..f5eac4a616761f00447706e87459e37312dca350 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -2507,24 +2507,28 @@ class JSFrontendAccess implements Frontend {
   }
 
   @override
-  bool hasResolvedAst(Element element) {
+  bool hasResolvedAst(ExecutableElement element) {
     if (element is SynthesizedCallMethodElementX) {
       return true;
     } else if (element is ConstructorBodyElementX) {
       return true;
     } else if (element is FieldElementX) {
       return true;
+    } else if (element is DeferredLoaderGetterElementX) {
+      return true;
     } else {
       return resolution.hasResolvedAst(element);
     }
   }
 
   @override
-  ResolvedAst getResolvedAst(Element element) {
+  ResolvedAst getResolvedAst(ExecutableElement element) {
     if (element is SynthesizedCallMethodElementX) {
       return element.resolvedAst;
     } else if (element is ConstructorBodyElementX) {
       return element.resolvedAst;
+    } else if (element is DeferredLoaderGetterElementX) {
+      return element.resolvedAst;
     } else if (element is FieldElementX) {
       // TODO(johnniwinther): Find a good invariant for resolution of fields.
       // Currently some but not all are resolved (maybe it has to do with