Deal with "classes" that don't belong to any library. Addresses issue 12231.

runtime/lib/mirrors.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "lib/invocation_mirror.h"
 #include "vm/bootstrap_natives.h"
 #include "vm/dart_entry.h"
 #include "vm/exceptions.h"
 #include "vm/object_store.h"
 #include "vm/port.h"
@@ skipping 344 matching lines @@
 DEFINE_NATIVE_ENTRY(ClassMirror_name, 1) {
   GET_NON_NULL_NATIVE_ARGUMENT(MirrorReference, ref, arguments->NativeArgAt(0));
   const Class& klass = Class::Handle(ref.GetClassReferent());
   return klass.UserVisibleName();
 }
 
 
 DEFINE_NATIVE_ENTRY(ClassMirror_library, 1) {
   GET_NON_NULL_NATIVE_ARGUMENT(MirrorReference, ref, arguments->NativeArgAt(0));
   const Class& klass = Class::Handle(ref.GetClassReferent());
-  return CreateLibraryMirror(Library::Handle(klass.library()));
+  const Library& library = Library::Handle(klass.library());
+  // TODO(rmacnak): Revisit when we decide what to do about
+  // reflectClass(dynamic).
+  if (library.IsNull()) {
+    return Instance::null();
+  }
+  return CreateLibraryMirror(library);
 }
 
 
 DEFINE_NATIVE_ENTRY(ClassMirror_supertype, 1) {
   GET_NON_NULL_NATIVE_ARGUMENT(MirrorReference, ref, arguments->NativeArgAt(0));
   const Class& klass = Class::Handle(ref.GetClassReferent());
   return klass.super_type();
 }
 
 
@@ skipping 811 matching lines @@
 
 DEFINE_NATIVE_ENTRY(VariableMirror_type, 1) {
   GET_NON_NULL_NATIVE_ARGUMENT(MirrorReference, ref, arguments->NativeArgAt(0));
   const Field& field = Field::Handle(ref.GetFieldReferent());
 
   const AbstractType& type = AbstractType::Handle(field.type());
   return CreateTypeMirror(type);
 }
 
 }  // namespace dart