Remove useless calls to v8::Value::ToString()

Source/bindings/v8/custom/V8WindowCustom.cpp

Index: Source/bindings/v8/custom/V8WindowCustom.cpp
diff --git a/Source/bindings/v8/custom/V8WindowCustom.cpp b/Source/bindings/v8/custom/V8WindowCustom.cpp
index 697bc83832f19f415a6c088bb85d374936ece5ad..100a1bf779367ae0279fca3afd2e808ea81f4df8 100644
--- a/Source/bindings/v8/custom/V8WindowCustom.cpp
+++ b/Source/bindings/v8/custom/V8WindowCustom.cpp
@@ -480,7 +480,7 @@ bool V8Window::namedSecurityCheckCustom(v8::Local<v8::Object> host, v8::Local<v8
         // We need to explicitly compare against nameOfProtoProperty because
         // V8's JSObject::LocalLookup finds __proto__ before
         // interceptors and even when __proto__ isn't a "real named property".
-        v8::Handle<v8::String> keyString = key->ToString();
+        v8::Handle<v8::String> keyString = key.As<v8::String>();
         if (type == v8::ACCESS_GET
             && childFrame
             && !host->HasRealNamedProperty(keyString)