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diff --git a/webkit/browser/fileapi/file_stream_writer.h b/webkit/browser/fileapi/file_stream_writer.h
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+++ b/webkit/browser/fileapi/file_stream_writer.h
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+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef WEBKIT_BROWSER_FILEAPI_FILE_STREAM_WRITER_H_
+#define WEBKIT_BROWSER_FILEAPI_FILE_STREAM_WRITER_H_
+
+#include "base/basictypes.h"
+#include "net/base/completion_callback.h"
+#include "webkit/storage/webkit_storage_export.h"
+
+namespace net {
+class IOBuffer;
+}
+
+namespace fileapi {
+
+// A generic interface for writing to a file-like object.
+class WEBKIT_STORAGE_EXPORT_PRIVATE FileStreamWriter {
+ public:
+  // Closes the file. If there's an in-flight operation, it is canceled (i.e.,
+  // the callback function associated with the operation is not called).
+  virtual ~FileStreamWriter() {}
+
+  // Writes to the current cursor position asynchronously.
+  //
+  // Up to buf_len bytes will be written.  (In other words, partial
+  // writes are allowed.) If the write completed synchronously, it returns
+  // the number of bytes written. If the operation could not be performed, it
+  // returns an error code. Otherwise, net::ERR_IO_PENDING is returned, and the
+  // callback will be run on the thread where Write() was called when the write
+  // has completed.
+  //
+  // This errors out (either synchronously or via callback) with:
+  //   net::ERR_FILE_NOT_FOUND: When the target file is not found.
+  //   net::ERR_ACCESS_DENIED: When the target file is a directory or
+  //      the writer has no permission on the file.
+  //   net::ERR_FILE_NO_SPACE: When the write will result in out of quota
+  //      or there is not enough room left on the disk.
+  //
+  // It is invalid to call Write while there is an in-flight async operation.
+  virtual int Write(net::IOBuffer* buf, int buf_len,
+                    const net::CompletionCallback& callback) = 0;
+
+  // Cancels an in-flight async operation.
+  //
+  // If the cancel is finished synchronously, it returns net::OK. If the
+  // cancel could not be performed, it returns an error code. Especially when
+  // there is no in-flight operation, net::ERR_UNEXPECTED is returned.
+  // Otherwise, net::ERR_IO_PENDING is returned, and the callback will be run on
+  // the thread where Cancel() was called when the cancel has completed. It is
+  // invalid to call Cancel() more than once on the same async operation.
+  //
+  // In either case, the callback function passed to the in-flight async
+  // operation is dismissed immediately when Cancel() is called, and thus
+  // will never be called.
+  virtual int Cancel(const net::CompletionCallback& callback) = 0;
+
+  // Flushes the data written so far.
+  //
+  // If the flush finished synchronously, it return net::OK. If the flush could
+  // not be performed, it returns an error code. Otherwise, net::ERR_IO_PENDING
+  // is returned, and the callback will be run on the thread where Flush() was
+  // called when the flush has completed.
+  //
+  // It is invalid to call Flush while there is an in-flight async operation.
+  virtual int Flush(const net::CompletionCallback& callback) = 0;
+};
+
+}  // namespace fileapi
+
+#endif  // WEBKIT_BROWSER_FILEAPI_FILE_STREAM_WRITER_H_