Implemented Document.contentType

Source/core/xml/XMLHttpRequest.cpp

Index: Source/core/xml/XMLHttpRequest.cpp
diff --git a/Source/core/xml/XMLHttpRequest.cpp b/Source/core/xml/XMLHttpRequest.cpp
index c043707688049ee47e6c2b286431a0b8c03a6bc4..1a7e5435f1b653355571929f6f154c736b66081c 100644
--- a/Source/core/xml/XMLHttpRequest.cpp
+++ b/Source/core/xml/XMLHttpRequest.cpp
@@ -242,7 +242,8 @@ Document* XMLHttpRequest::responseXML(ExceptionState& exceptionState)
         return 0;
 
     if (!m_createdDocument) {
-        bool isHTML = equalIgnoringCase(responseMIMEType(), "text/html");
+        AtomicString mimeType = responseMIMEType();
+        bool isHTML = equalIgnoringCase(mimeType, "text/html");
 
         // The W3C spec requires the final MIME type to be some valid XML type, or text/html.
         // If it is text/html, then the responseType of "document" must have been supplied explicitly.
@@ -260,6 +261,7 @@ Document* XMLHttpRequest::responseXML(ExceptionState& exceptionState)
             m_responseDocument->setContent(m_responseText.flattenToString());
             m_responseDocument->setSecurityOrigin(securityOrigin());
             m_responseDocument->setContextFeatures(document()->contextFeatures());
+            m_responseDocument->setMimeType(mimeType);
             if (!m_responseDocument->wellFormed())
                 m_responseDocument = nullptr;
         }