URLFetcher won't call delegate until file is closed.

net/base/file_stream_context_win.cc

 // 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.
 
 #include "net/base/file_stream_context.h"
 
 #include <windows.h>
 
 #include "base/files/file_path.h"
 #include "base/logging.h"
@@ skipping 178 matching lines @@
   return IOResult::FromOSError(GetLastError());
 }
 
 FileStream::Context::IOResult FileStream::Context::FlushFileImpl() {
   if (FlushFileBuffers(file_))
     return IOResult(OK, 0);
 
   return IOResult::FromOSError(GetLastError());
 }
 
+FileStream::Context::IOResult FileStream::Context::CloseFileImpl() {
+  bool success = base::ClosePlatformFile(file_);
+  file_ = base::kInvalidPlatformFileValue;
+  if (success)
+    return IOResult(OK, 0);
+
+  return IOResult::FromOSError(GetLastError());
+}
+
 void FileStream::Context::IOCompletionIsPending(
     const CompletionCallback& callback,
     IOBuffer* buf) {
   DCHECK(callback_.is_null());
   callback_ = callback;
   in_flight_buf_ = buf;  // Hold until the async operation ends.
   async_in_progress_ = true;
 }
 
 void FileStream::Context::OnIOCompleted(
@@ skipping 25 matching lines @@
   }
 
   CompletionCallback temp_callback = callback_;
   callback_.Reset();
   scoped_refptr<IOBuffer> temp_buf = in_flight_buf_;
   in_flight_buf_ = NULL;
   temp_callback.Run(result);
 }
 
 }  // namespace net