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

Source/bindings/core/v8/ScriptValue.h

 /*
  * Copyright (C) 2008, 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 23 matching lines @@
 #include "bindings/core/v8/ScriptState.h"
 #include "bindings/core/v8/SharedPersistent.h"
 #include "core/CoreExport.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefPtr.h"
 #include "wtf/text/WTFString.h"
 #include <v8.h>
 
 namespace blink {
 
+class ExceptionState;
 class JSONValue;
 
+template <typename T>
+T script_value_cast(const v8::Local<v8::Value>&, v8::Isolate*, ExceptionState&);
+
 class CORE_EXPORT ScriptValue final {
 public:
     template<typename T>
     static ScriptValue from(ScriptState* scriptState, T value)
     {
         return ScriptValue(scriptState, toV8(value, scriptState->context()->Global(), scriptState->isolate()));
     }
 
+    template<typename T>
+    T to(ExceptionState& exceptionState) const
+    {
+        return script_value_cast<T>(v8Value(), isolate(), exceptionState);

[haraken, 2015/03/14 01:27:19]

I'm wondering why we cannot simply call:

  NativeValueTraits<T>::nativeValue(v8Value(), isolate, exceptionState);

+    }
+
     ScriptValue() { }
 
     ScriptValue(ScriptState* scriptState, v8::Handle<v8::Value> value)
         : m_scriptState(scriptState)
         , m_value(value.IsEmpty() ? nullptr : SharedPersistent<v8::Value>::create(value, scriptState->isolate()))
     {
         ASSERT(isEmpty() || m_scriptState);
     }
 
     ScriptValue(const ScriptValue& value)
@@ skipping 87 matching lines @@
     static ScriptValue createNull(ScriptState*);
 
 private:
     RefPtr<ScriptState> m_scriptState;
     RefPtr<SharedPersistent<v8::Value>> m_value;
 };
 
 } // namespace blink
 
 #endif // ScriptValue_h