Add ftplugin for gn filetype

The 'includeexpr' setting (and corresponding autoload function) allows
users to jump from one gn file to another with the 'gf' command (as long
as vim's cwd is set to /src/).

The commentstring setting lets vim know what the correct comments are
for gn files (this integrates nicely with plugins like vim-commentary).

BUG=

Review-Url: https://codereview.chromium.org/2654673002
Cr-Original-Commit-Position: refs/heads/master@{#445782}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 23449b77810518956542fb0b65be9da863e8492a
2 files changed
tree: 8ce30d96103c789b89c290230a4b6b2f4e8ed511
  1. tools/