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

storage/browser/fileapi/local_file_stream_reader.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 "storage/browser/fileapi/local_file_stream_reader.h"
 
 #include "base/files/file_util.h"
 #include "base/files/file_util_proxy.h"
 #include "base/location.h"
 #include "base/logging.h"
@@ skipping 88 matching lines @@
 }
 
 void LocalFileStreamReader::DidOpenFileStream(
     const net::CompletionCallback& callback,
     int result) {
   if (result != net::OK) {
     callback.Run(result);
     return;
   }
   result = stream_impl_->Seek(
-      base::File::FROM_BEGIN, initial_offset_,
-      base::Bind(&LocalFileStreamReader::DidSeekFileStream,
-                 weak_factory_.GetWeakPtr(),
-                 callback));
+      initial_offset_, base::Bind(&LocalFileStreamReader::DidSeekFileStream,
+                                  weak_factory_.GetWeakPtr(), callback));
   if (result != net::ERR_IO_PENDING) {
     callback.Run(result);
   }
 }
 
 void LocalFileStreamReader::DidSeekFileStream(
     const net::CompletionCallback& callback,
     int64 seek_result) {
   if (seek_result < 0) {
     callback.Run(static_cast<int>(seek_result));
@@ skipping 37 matching lines @@
     return;
   }
   if (!VerifySnapshotTime(expected_modification_time_, file_info)) {
     callback.Run(net::ERR_UPLOAD_FILE_CHANGED);
     return;
   }
   callback.Run(file_info.size);
 }
 
 }  // namespace storage