Fix crash when deferred loading would encounter an unresolved super setter.

pkg/compiler/lib/src/deferred_load.dart

Index: pkg/compiler/lib/src/deferred_load.dart
diff --git a/pkg/compiler/lib/src/deferred_load.dart b/pkg/compiler/lib/src/deferred_load.dart
index 378710d85f6b94ca58399d62be5a9ddd91e25323..fd1f77c4ec5fa6413a339ebf57ca5957b225972b 100644
--- a/pkg/compiler/lib/src/deferred_load.dart
+++ b/pkg/compiler/lib/src/deferred_load.dart
@@ -246,6 +246,11 @@ class DeferredLoadTask extends CompilerTask {
       Set<ConstantValue> constants,
       isMirrorUsage) {
 
+    if (element.isErroneous) {
+      // Erroneous elements are ignored.
+      return;
+    }
+
     /// Recursively collects all the dependencies of [type].
     void collectTypeDependencies(DartType type) {
       if (type is GenericType) {