Make FileStream::Seek async and add FileStream::SeekSync for sync operation

webkit/blob/blob_url_request_job.cc

Index: webkit/blob/blob_url_request_job.cc
diff --git a/webkit/blob/blob_url_request_job.cc b/webkit/blob/blob_url_request_job.cc
index ccc229cea1f87f5379675079b7bdc5a8c1ac4691..d6be8a5a0443b085c941e096784f2c7431f6b7bb 100644
--- a/webkit/blob/blob_url_request_job.cc
+++ b/webkit/blob/blob_url_request_job.cc
@@ -385,10 +385,10 @@ void BlobURLRequestJob::DidOpenFile(int bytes_to_read,
 
   const BlobData::Item& item = blob_data_->items().at(current_item_index_);
   {
-    // stream_.Seek() blocks the IO thread, see http://crbug.com/75548.
+    // stream_.SeekSync() blocks the IO thread, see http://crbug.com/75548.
     base::ThreadRestrictions::ScopedAllowIO allow_io;
     int64 offset = current_item_offset_ + static_cast<int64>(item.offset);
-    if (offset > 0 && offset != stream_->Seek(net::FROM_BEGIN, offset)) {
+    if (offset > 0 && offset != stream_->SeekSync(net::FROM_BEGIN, offset)) {
       NotifyFailure(net::ERR_FAILED);
       return;
     }