[net] Cleanup filename_util and make it portable.

chrome/browser/download/download_target_determiner.cc

Index: chrome/browser/download/download_target_determiner.cc
diff --git a/chrome/browser/download/download_target_determiner.cc b/chrome/browser/download/download_target_determiner.cc
index ad40bc067a679bb3e6b3eaa8a9ad713907ba75be..e19d7ef96038d25e85894798919dec24aec68804 100644
--- a/chrome/browser/download/download_target_determiner.cc
+++ b/chrome/browser/download/download_target_determiner.cc
@@ -269,10 +269,8 @@ void DownloadTargetDeterminer::NotifyExtensionsDone(
     // Downloads/music/music/music/bar.mp3.
     base::FilePath new_path(download_prefs_->DownloadPath().Append(
         suggested_path).NormalizePathSeparators());
-    // Do not pass a mime type to GenerateSafeFileName so that it does not force
-    // the filename to have an extension if the (Chrome) extension does not
-    // suggest it.
-    net::GenerateSafeFileName(std::string(), false, &new_path);
+    net::EnsureSafePortableFileName(
+        std::string(), net::EXTENSION_OPTION_KEEP_EXISTING, &new_path);
     virtual_path_ = new_path;
     create_target_directory_ = true;
   }