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..95298b5de7e62016caa4c12496565c48e618baef 100644
--- a/content/browser/download/download_file_impl.cc
+++ b/content/browser/download/download_file_impl.cc
@@ -74,12 +74,10 @@ void DownloadFileImpl::Initialize(const InitializeCallback& callback) {
 
   update_timer_.reset(new base::RepeatingTimer());
   DownloadInterruptReason result =
-      file_.Initialize(save_info_->file_path,
-                       default_download_directory_,
-                       std::move(save_info_->file),
-                       save_info_->offset,
+      file_.Initialize(save_info_->file_path, default_download_directory_,
+                       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));
@@ -112,7 +110,7 @@ DownloadInterruptReason DownloadFileImpl::AppendDataToFile(
                          this, &DownloadFileImpl::SendUpdate);
   }
   rate_estimator_.Increment(data_len);
-  return file_.AppendDataToFile(data, data_len);
+  return file_.WriteDataToFile(data, data_len);
 }
 
 void DownloadFileImpl::RenameAndUniquify(