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

chrome/browser/chromeos/drive/local_file_reader.cc

Index: chrome/browser/chromeos/drive/local_file_reader.cc
diff --git a/chrome/browser/chromeos/drive/local_file_reader.cc b/chrome/browser/chromeos/drive/local_file_reader.cc
index b1ff64d73b99273f95e2d435d812202fb860f910..ca2dfa2f87639b04e708b254c763f38549535615 100644
--- a/chrome/browser/chromeos/drive/local_file_reader.cc
+++ b/chrome/browser/chromeos/drive/local_file_reader.cc
@@ -52,10 +52,9 @@ void LocalFileReader::DidOpen(const net::CompletionCallback& callback,
   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);
 }