[bindings] Introduce ScriptValue.to<T> to convert to native values.

Source/bindings/core/v8/NativeValueTraits.h

Index: Source/bindings/core/v8/NativeValueTraits.h
diff --git a/Source/bindings/core/v8/NativeValueTraits.h b/Source/bindings/core/v8/NativeValueTraits.h
new file mode 100644
index 0000000000000000000000000000000000000000..fc95a817db80b03de527265b792f0c03925de88b
--- /dev/null
+++ b/Source/bindings/core/v8/NativeValueTraits.h
@@ -0,0 +1,21 @@
+// Copyright (c) 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 NativeValueTraits_h
+#define NativeValueTraits_h
+
+#include <v8.h>
+
+namespace blink {
+
+class ExceptionState;
+
+template <typename T>
+struct NativeValueTraits {
+    static T nativeValue(const v8::Local<v8::Value>&, v8::Isolate*, ExceptionState&);
+};
+
+} // namespace blink
+
+#endif // NativeValueTraits_h