gn: some vim support files

tools/gn/misc/vim/ftdetect/gnfiletype.vim

Index: tools/gn/misc/vim/ftdetect/gnfiletype.vim
diff --git a/tools/gn/misc/vim/ftdetect/gnfiletype.vim b/tools/gn/misc/vim/ftdetect/gnfiletype.vim
new file mode 100644
index 0000000000000000000000000000000000000000..d7bf55cc1287c4deb21bf7b2b98eca3def8b6555
--- /dev/null
+++ b/tools/gn/misc/vim/ftdetect/gnfiletype.vim
@@ -0,0 +1,27 @@
+" Copyright 2014 The Chromium Authors. All rights reserved.
+" Use of this source code is governed by a BSD-style license that can be
+" found in the LICENSE file.
+
+" We take care to preserve the user's fileencodings and fileformats,
+" because those settings are global (not buffer local), yet we want
+" to override them for loading GN files, which should be UTF-8.
+let s:current_fileformats = ''
+let s:current_fileencodings = ''
+
+" define fileencodings to open as utf-8 encoding even if it's ascii.
+function! s:gnfiletype_pre()
+  let s:current_fileformats = &g:fileformats
+  let s:current_fileencodings = &g:fileencodings
+  set fileencodings=utf-8 fileformats=unix
+  setlocal filetype=gn
+endfunction
+
+" restore fileencodings as others
+function! s:gnfiletype_post()
+  let &g:fileformats = s:current_fileformats
+  let &g:fileencodings = s:current_fileencodings
+endfunction
+
+au BufNewFile *.gn setlocal filetype=gn fileencoding=utf-8 fileformat=unix
+au BufRead *.gn call s:gnfiletype_pre()
+au BufReadPost *.gn call s:gnfiletype_post()