Saves time over multiple deploys.
in case anyone wants to pick this up: according to this blogpost (http://blog.yjl.im/2012/03/downloading-only-when-modified-using.html) we should be able to fix this issue quite easily using something like this:
curl https://github.com/selkhateeb/heroku-vagrant-dart-build/releases/download/1.2.0-dev.1.0/dart-sdk.tar -z dart-sdk.tar -o dart-sdk.tar -v
however, i wasn't able to reproduce correct behavior on my computer. maybe it's just github not supporting the If-Modified-Since-header...
If you use an url like https://storage.googleapis.com/dart-archive/channels/stable/release/latest/editor/darteditor-linux-x64.zip, you want to refresh each time the sdk (as you are linked to the latest darteditor) .