Only support seeking file streams from the beginning of the file.

chrome/browser/chromeos/drive/local_file_reader.cc

 // Copyright 2013 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 "chrome/browser/chromeos/drive/local_file_reader.h"
 
 #include "base/bind.h"
 #include "base/files/file_path.h"
 #include "base/sequenced_task_runner.h"
 #include "net/base/completion_callback.h"
@@ skipping 34 matching lines @@
   int rv = file_stream_.Read(in_buffer, buffer_length, callback);
   DCHECK_EQ(rv, net::ERR_IO_PENDING);
 }
 
 void LocalFileReader::DidOpen(const net::CompletionCallback& callback,
                               int64 offset,
                               int error) {
   if (error != net::OK)
     return callback.Run(error);
 
-  int rv = file_stream_.Seek(base::File::FROM_BEGIN, offset,
-                             Bind(&LocalFileReader::DidSeek,
-                                  weak_ptr_factory_.GetWeakPtr(),
-                                  callback, offset));
+  int rv = file_stream_.Seek(
+      offset, Bind(&LocalFileReader::DidSeek, weak_ptr_factory_.GetWeakPtr(),
+                   callback, offset));
   DCHECK_EQ(rv, net::ERR_IO_PENDING);
 }
 
 void LocalFileReader::DidSeek(const net::CompletionCallback& callback,
                               int64 offset,
                               int64 error) {
   callback.Run(error == offset ? net::OK : net::ERR_FAILED);
 }
 
 }  // namespace util
 }  // namespace drive