Refactor BaseFile class to support sparse files

content/browser/download/download_file_impl.cc

Index: content/browser/download/download_file_impl.cc
diff --git a/content/browser/download/download_file_impl.cc b/content/browser/download/download_file_impl.cc
index 7e8a3f0c5099ca3e95a906585b21988a766217e8..b5817e3ec252d5fb0d884b68271d3bdeebae148d 100644
--- a/content/browser/download/download_file_impl.cc
+++ b/content/browser/download/download_file_impl.cc
@@ -79,7 +79,8 @@ void DownloadFileImpl::Initialize(const InitializeCallback& callback) {
                        std::move(save_info_->file),
                        save_info_->offset,
                        save_info_->hash_of_partial_file,
-                       std::move(save_info_->hash_state));
+                       std::move(save_info_->hash_state),
+                       BaseFile::EXCLUSIVE);
   if (result != DOWNLOAD_INTERRUPT_REASON_NONE) {
     BrowserThread::PostTask(
         BrowserThread::UI, FROM_HERE, base::Bind(callback, result));