Add json responseType support to XMLHttpRequest

Source/core/xml/XMLHttpRequest.h

Index: Source/core/xml/XMLHttpRequest.h
diff --git a/Source/core/xml/XMLHttpRequest.h b/Source/core/xml/XMLHttpRequest.h
index fde3a84be50dc828ba69a830a38d5149ddbab9f5..6f50ea30e4fb675c545730e664ed9a6cd63eecbc 100644
--- a/Source/core/xml/XMLHttpRequest.h
+++ b/Source/core/xml/XMLHttpRequest.h
@@ -69,6 +69,7 @@ public:
     enum ResponseTypeCode {
         ResponseTypeDefault,
         ResponseTypeText,
+        ResponseTypeJson,
         ResponseTypeDocument,
         ResponseTypeBlob,
         ResponseTypeArrayBuffer
@@ -107,6 +108,7 @@ public:
     String getAllResponseHeaders(ExceptionState&) const;
     String getResponseHeader(const AtomicString& name, ExceptionState&) const;
     ScriptString responseText(ExceptionState&);
+    ScriptString responseJsonSource(ExceptionState&);
     Document* responseXML(ExceptionState&);
     Blob* responseBlob(ExceptionState&);
     unsigned long timeout() const { return m_timeoutMilliseconds; }