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

storage/browser/fileapi/local_file_stream_reader.cc

Index: storage/browser/fileapi/local_file_stream_reader.cc
diff --git a/storage/browser/fileapi/local_file_stream_reader.cc b/storage/browser/fileapi/local_file_stream_reader.cc
index 90d4a461587768a318604447c0b1d56f821336d6..e8473eb7568e798438e839e4f30b12456f7229c4 100644
--- a/storage/browser/fileapi/local_file_stream_reader.cc
+++ b/storage/browser/fileapi/local_file_stream_reader.cc
@@ -106,10 +106,8 @@ void LocalFileStreamReader::DidOpenFileStream(
     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);
   }