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

net/base/file_stream.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/file_stream.h"
 
 #include "base/profiler/scoped_tracker.h"
 #include "net/base/file_stream_context.h"
 #include "net/base/net_errors.h"
 
@@ skipping 26 matching lines @@
 
 int FileStream::Close(const CompletionCallback& callback) {
   context_->Close(callback);
   return ERR_IO_PENDING;
 }
 
 bool FileStream::IsOpen() const {
   return context_->file().IsValid();
 }
 
-int FileStream::Seek(base::File::Whence whence,
-                     int64 offset,
-                     const Int64CompletionCallback& callback) {
+int FileStream::Seek(int64 offset, const Int64CompletionCallback& callback) {
   if (!IsOpen())
     return ERR_UNEXPECTED;
 
-  context_->Seek(whence, offset, callback);
+  context_->Seek(offset, callback);
   return ERR_IO_PENDING;
 }
 
 int FileStream::Read(IOBuffer* buf,
                      int buf_len,
                      const CompletionCallback& callback) {
   // TODO(rvargas): Remove ScopedTracker below once crbug.com/475751 is fixed.
   tracked_objects::ScopedTracker tracking_profile(
       FROM_HERE_WITH_EXPLICIT_FUNCTION("475751 FileStream::Read"));
 
@@ skipping 22 matching lines @@
 
   context_->Flush(callback);
   return ERR_IO_PENDING;
 }
 
 const base::File& FileStream::GetFileForTesting() const {
   return context_->file();
 }
 
 }  // namespace net