Move FileEnumerator to its own file, do some refactoring.

net/url_request/url_request_file_job.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 loading files, we make use of overlapped i/o to ensure that reading from
 // the filesystem (e.g., a network filesystem) does not block the calling
 // thread.  An alternative approach would be to use a background thread or pool
 // of threads, but it seems better to leverage the operating system's ability
 // to do background file reads for us.
 //
 // Since overlapped reads require a 'static' buffer for the duration of the
 // asynchronous read, the URLRequestFileJob keeps a buffer as a member var.  In
 // URLRequestFileJob::Read, data is simply copied from the object's buffer into
 // the given buffer.  If there is no data to copy, the URLRequestFileJob
 // attempts to read more from the file to fill its buffer.  If reading from the
 // file does not complete synchronously, then the URLRequestFileJob waits for a
 // signal from the OS that the overlapped read has completed.  It does so by
 // leveraging the MessageLoop::WatchObject API.
 
 #include "net/url_request/url_request_file_job.h"
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
+#include "base/file_util.h"
 #include "base/message_loop.h"
 #include "base/platform_file.h"
 #include "base/string_util.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/worker_pool.h"
 #include "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
 #include "googleurl/src/gurl.h"
 #include "net/base/file_stream.h"
 #include "net/base/io_buffer.h"
@@ skipping 256 matching lines @@
     NotifyDone(URLRequestStatus(URLRequestStatus::FAILED, result));
   }
 
   remaining_bytes_ -= result;
   DCHECK_GE(remaining_bytes_, 0);
 
   NotifyReadComplete(result);
 }
 
 }  // namespace net