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 9639d947738e4351dbcbfe6a1e90e09c3a577bef..5344fa2fc3c1c43144123166791a0eff56f6a7bc 100644
--- a/Source/core/xml/XMLHttpRequest.h
+++ b/Source/core/xml/XMLHttpRequest.h
@@ -150,6 +150,14 @@ 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>);
 
@@ -166,6 +174,8 @@ 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.
@@ -244,6 +254,7 @@ private:
     PersistentWillBeMember<UnderlyingSource> m_streamSource;
 
     RefPtr<ThreadableLoader> m_loader;
+    unsigned long m_loaderIdentifier;
     State m_state;
 
     ResourceResponse m_response;