Make it possible to pull in vim-codesearch via chromium/src/tools/vim

[asankah]

Let it be possible to pull in the plugin via something like:

so `=path_to_chrome . 'tools/vim/vim-codesearch.vim'`

[asankah]

On option is to:

• perform regular releases that push out an archive
• src.git's tools/vim/vim-codesearch.vim pulls in, expands and uses (if out of date, or if there's no checkout found in the default location).
  • Probably don't want to do network IO on every editor startup. Hence we could do a two stage A-B style updates that don't trample running instances of Vim.