Use the async version of WebFileSystem::createFileWriter

Source/web/AsyncFileWriterChromium.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 29 matching lines @@
 class WebFileWriter;
 }
 
 namespace WebCore {
 
 class Blob;
 class AsyncFileWriterClient;
 
 class AsyncFileWriterChromium : public AsyncFileWriter, public WebKit::WebFileWriterClient {
 public:
-    AsyncFileWriterChromium(AsyncFileWriterClient* client);
-    ~AsyncFileWriterChromium();
-    
+    static PassOwnPtr<AsyncFileWriterChromium> create(AsyncFileWriterClient*);
+    virtual ~AsyncFileWriterChromium();
+
     void setWebFileWriter(PassOwnPtr<WebKit::WebFileWriter> writer);
 
     // FileWriter
     virtual void write(long long position, Blob* data);
     virtual void truncate(long long length);
     virtual void abort();
 
     // WebFileWriterClient
     virtual void didWrite(long long bytes, bool complete);
     virtual void didTruncate();
     virtual void didFail(WebKit::WebFileError);
 
 private:
+    explicit AsyncFileWriterChromium(AsyncFileWriterClient*);
+
     OwnPtr<WebKit::WebFileWriter> m_writer;
     AsyncFileWriterClient* m_client;
 };
 
 } // namespace
 
 #endif // AsyncFileWriterChromium_h