[net] Cleanup filename_util and make it portable.

content/browser/download/save_package.cc

Index: content/browser/download/save_package.cc
diff --git a/content/browser/download/save_package.cc b/content/browser/download/save_package.cc
index 8300c2d95b2b13d568acd91085b973af4d129fb1..64758792460709acd80b90c030059719660e5701 100644
--- a/content/browser/download/save_package.cc
+++ b/content/browser/download/save_package.cc
@@ -1402,10 +1402,9 @@ void SavePackage::OnPathPicked(
          (type == SAVE_PAGE_TYPE_AS_COMPLETE_HTML)) << type;
   // Ensure the filename is safe.
   saved_main_file_path_ = final_name;
-  // TODO(asanka): This call may block on IO and shouldn't be made
-  // from the UI thread.  See http://crbug.com/61827.
-  net::GenerateSafeFileName(web_contents()->GetContentsMimeType(), false,
-                            &saved_main_file_path_);
+  net::EnsureSafePortableFileName(std::string(),
+                                  net::EXTENSION_OPTION_KEEP_EXISTING,
+                                  &saved_main_file_path_);
 
   saved_main_directory_path_ = saved_main_file_path_.DirName();
   save_type_ = type;