ParentNode#appendChild(null) shouldn't crash

sky/engine/tonic/dart_exception_factory.h

Index: sky/engine/tonic/dart_exception_factory.h
diff --git a/sky/engine/tonic/dart_exception_factory.h b/sky/engine/tonic/dart_exception_factory.h
new file mode 100644
index 0000000000000000000000000000000000000000..bb6e4636a0bb45ab4528a08522d3e688a215987a
--- /dev/null
+++ b/sky/engine/tonic/dart_exception_factory.h
@@ -0,0 +1,29 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SKY_ENGINE_TONIC_DART_EXCEPTION_FACTORY_H_
+#define SKY_ENGINE_TONIC_DART_EXCEPTION_FACTORY_H_
+
+#include "dart/runtime/include/dart_api.h"
+#include "sky/engine/tonic/dart_persistent_value.h"
+#include "sky/engine/wtf/text/WTFString.h"
+
+namespace blink {
+class DartState;
+
+class DartExceptionFactory {
+ public:
+  explicit DartExceptionFactory(DartState* dart_state);
+  ~DartExceptionFactory();
+
+  Dart_Handle CreateException(const String& class_name, const String& message);
+
+ private:
+  DartState* dart_state_;
+  DartPersistentValue core_library_;
+};
+
+}  // namespace blink
+
+#endif  // SKY_ENGINE_TONIC_DART_EXCEPTION_FACTORY_H_