Add toWebCoreString() / toWebCoreAtomicString() overloads taking a v8::String

Source/bindings/v8/ScriptPreprocessor.cpp

Index: Source/bindings/v8/ScriptPreprocessor.cpp
diff --git a/Source/bindings/v8/ScriptPreprocessor.cpp b/Source/bindings/v8/ScriptPreprocessor.cpp
index 1d5b8428eb10e8ecf5504b0be771bc8ef9d196c6..efc2bdd779c141a9eed59d7add0689e6aa230fe3 100644
--- a/Source/bindings/v8/ScriptPreprocessor.cpp
+++ b/Source/bindings/v8/ScriptPreprocessor.cpp
@@ -104,7 +104,7 @@ String ScriptPreprocessor::preprocessSourceCode(const String& sourceCode, const
     v8::Handle<v8::Value> resultValue = V8ScriptRunner::callAsFunction(m_preprocessorFunction.newLocal(m_isolate), m_context.newLocal(m_isolate)->Global(), WTF_ARRAY_LENGTH(argv), argv);
 
     if (!resultValue.IsEmpty() && resultValue->IsString())
-        return toWebCoreStringWithNullCheck(resultValue);
+        return toWebCoreStringWithNullCheck(resultValue.As<v8::String>());
 
     return sourceCode;
 }