Improve vim's 'gf' for BUILD.gn files

If vim-maktaba is installed, vim will use it during the 'gf' command in
GN files.

If maktaba is not installed, the plugin uses a fallback approach,
however this is easily broken with the 'autochdir' setting.

BUG=

Review-Url: https://codereview.chromium.org/2657853004
Cr-Original-Commit-Position: refs/heads/master@{#446447}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: e46620f101019c220a303e6cc82c57c928a677bd
1 file changed
tree: ffed8ee2880c1b1fc5aa8ff05207d4c5afe50efa
  1. tools/