Using DIR_DEFAULT_DOWNLOADS_SAFE when DIR_DEFAULT_DOWNLOADS got home

directory or desktop

fix brave/browser-laptop#13229
fix brave/browser-laptop#13255

Auditors: @bridiver, @bsclifton

atom/browser/api/atom_api_dialog.cc

@@ -86,6 +86,23 @@ struct Converter<file_dialog::DialogSettings> {
 
 namespace {
 
+// Consider downloads 'dangerous' if they go to the home directory on Linux and
+// to the desktop on any platform.
+bool DownloadPathIsDangerous(const base::FilePath& download_path) {
+#if defined(OS_LINUX)
+  base::FilePath home_dir = base::GetHomeDir();
+  if (download_path == home_dir) {
+    return true;
+  }
+#endif
+  base::FilePath desktop_dir;
+  if (!PathService::Get(base::DIR_USER_DESKTOP, &desktop_dir)) {
+    NOTREACHED();
+    return false;
+  }
+  return (download_path == desktop_dir);
+}
+
 void ShowMessageBox(int type,
                     const std::vector<std::string>& buttons,
                     int default_id,
@@ -151,7 +168,16 @@ void ShowDialog(const file_dialog::DialogSettings& settings,
 
   base::FilePath default_path = settings.default_path;
   if (default_path.empty()) {
-    PathService::Get(chrome::DIR_DEFAULT_DOWNLOADS, &default_path);
+    if (!PathService::Get(chrome::DIR_DEFAULT_DOWNLOADS, &default_path)) {
+      NOTREACHED();
+    }
+  }
+  if (DownloadPathIsDangerous(default_path)) {
+    // This is only useful on platforms that support
+    // DIR_DEFAULT_DOWNLOADS_SAFE.
+    if (!PathService::Get(chrome::DIR_DEFAULT_DOWNLOADS_SAFE, &default_path)) {
+      NOTREACHED();
+    }
   }
   file_type_info.include_all_files = settings.include_all_files;
   file_type_info.extension_description_overrides =