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

net/base/upload_file_element_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 "net/base/upload_file_element_reader.h"
 
 #include "base/bind.h"
 #include "base/files/file_util.h"
 #include "base/location.h"
 #include "base/task_runner_util.h"
@@ skipping 96 matching lines @@
 
   if (result < 0) {
     DLOG(WARNING) << "Failed to open \"" << path_.value()
                   << "\" for reading: " << result;
     callback.Run(result);
     return;
   }
 
   if (range_offset_) {
     int seek_result = file_stream_->Seek(
-        base::File::FROM_BEGIN, range_offset_,
-        base::Bind(&UploadFileElementReader::OnSeekCompleted,
-                   weak_ptr_factory_.GetWeakPtr(), callback));
+        range_offset_, base::Bind(&UploadFileElementReader::OnSeekCompleted,
+                                  weak_ptr_factory_.GetWeakPtr(), callback));
     DCHECK_GT(0, seek_result);
     if (seek_result != ERR_IO_PENDING)
       callback.Run(seek_result);
   } else {
     OnSeekCompleted(callback, OK);
   }
 }
 
 void UploadFileElementReader::OnSeekCompleted(
     const CompletionCallback& callback,
@@ skipping 75 matching lines @@
     ScopedOverridingContentLengthForTests(uint64_t value) {
   overriding_content_length = value;
 }
 
 UploadFileElementReader::ScopedOverridingContentLengthForTests::
 ~ScopedOverridingContentLengthForTests() {
   overriding_content_length = 0;
 }
 
 }  // namespace net