URLFetcher won't call delegate until file is closed.

net/base/file_stream_context_posix.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.
 
 // For 64-bit file access (off_t = off64_t, lseek64, etc).
 #define _FILE_OFFSET_BITS 64
 
 #include "net/base/file_stream_context.h"
 
 #include <errno.h>
@@ skipping 166 matching lines @@
 FileStream::Context::IOResult FileStream::Context::WriteFileImpl(
     scoped_refptr<IOBuffer> buf,
     int buf_len) {
   ssize_t res = HANDLE_EINTR(write(file_, buf->data(), buf_len));
   if (res == -1)
     return IOResult::FromOSError(errno);
 
   return IOResult(res, 0);
 }
 
+FileStream::Context::IOResult FileStream::Context::CloseFileImpl() {
+  bool success = base::ClosePlatformFile(file_);
+  file_ = base::kInvalidPlatformFileValue;
+  if (!success)
+    return IOResult::FromOSError(errno);
+
+  return IOResult(OK, 0);
+}
+
 }  // namespace net