Squashed 'vim/bundle/dart/' content from commit 58984d5

git-subtree-dir: vim/bundle/dart
git-subtree-split: 58984d50c69cefa52558e78247b23a5de2c008f9
Merge commit 'ef0621a0d461ff493baa4873012868b21db3f7f5' as 'vim/bundle/dart'
Add 'it', 'desc', 'expect' and 'umd' JavaScript snippets