URLFetcher won't call delegate until file is closed.

net/base/file_stream.h

 // 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.
 
 // This file defines FileStream, a basic interface for reading and writing files
 // synchronously or asynchronously with support for seeking to an offset.
 // Note that even when used asynchronously, only one operation is supported at
 // a time.
 
 #ifndef NET_BASE_FILE_STREAM_H_
@@ skipping 63 matching lines @@
 
   // Call this method to open the FileStream synchronously.
   // The remaining methods cannot be used unless this method returns OK.  If
   // the file cannot be opened then an error code is returned.  open_flags is
   // a bitfield of base::PlatformFileFlags
   //
   // If the file stream is not closed manually, the underlying file will be
   // automatically closed when FileStream is destructed.
   virtual int OpenSync(const base::FilePath& path, int open_flags);
 
+  // Returns ERR_IO_PENDING and closes the file asynchronously, calling
+  // |callback| when done.
+  // It is invalid to request any asynchronous operations while there is an
+  // in-flight asynchronous operation.
+  virtual int Close(const CompletionCallback& callback);
+
+  // Closes the file immediately and returns OK. If the file is open
+  // asynchronously, Close(const CompletionCallback&) should be used instead.
+  virtual int CloseSync();
+
   // Returns true if Open succeeded and Close has not been called.
   virtual bool IsOpen() const;
 
   // Adjust the position from where data is read asynchronously.
   // Upon success, ERR_IO_PENDING is returned and |callback| will be run
   // on the thread where Seek() was called with the the stream position
   // relative to the start of the file.  Otherwise, an error code is returned.
   // It is invalid to request any asynchronous operations while there is an
   // in-flight asynchronous operation.
   virtual int Seek(Whence whence, int64 offset,
@@ skipping 152 matching lines @@
   // delaying FileStream's destructor. To perform all that separate object is
   // necessary.
   scoped_ptr<Context> context_;
 
   DISALLOW_COPY_AND_ASSIGN(FileStream);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_FILE_STREAM_H_