Make XHR use the background HTML parser

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 15484a4f1c3ebeb52cfb2f28cf9a3cfb5aea0783..b18581c42f9c58f1434920cad64b80d9dd6e42e5 100644
--- a/Source/core/xml/XMLHttpRequest.h
+++ b/Source/core/xml/XMLHttpRequest.h
@@ -149,6 +149,13 @@ public:
 
     virtual void trace(Visitor*) OVERRIDE;
 
+    static XMLHttpRequest* findInstancePendingDocumentParse(Document*);
+
+    // This is only to be called from |Document::finishedParsing|.
+    // When we use the off-thread HTML parser, we don't have a complete document just after |HTMLDocumentParser::finish()|.
+    // This method is used to notify that the response document is completely built.
+    void didFinishParsingDocument();
+
 private:
     XMLHttpRequest(ExecutionContext*, PassRefPtr<SecurityOrigin>);
 
@@ -165,6 +172,8 @@ private:
     virtual void didFail(const ResourceError&) OVERRIDE;
     virtual void didFailRedirectCheck() OVERRIDE;
 
+    void endLoading();
+
     // Returns the MIME type part of m_mimeTypeOverride if present and
     // successfully parsed, or returns one of the "Content-Type" header value
     // of the received response.
@@ -243,6 +252,7 @@ private:
     PersistentWillBeMember<UnderlyingSource> m_streamSource;
 
     RefPtr<ThreadableLoader> m_loader;
+    unsigned long m_loaderIdentifier;
     State m_state;
 
     ResourceResponse m_response;