support user-agent specific transformations in pub #50
Description
<img src="https://avatars.githubusercontent.com/u/2049220?v=3" align="left" width="96" height="96"hspace="10"> Issue by sigmundch
Originally opened as dart-lang/sdk#19169
[I'm creating this bug so we can gather our ideas or have a place we can point at from other bugs.]
We have many transformers that are only needed at deployment and not at development time.
One example are the polymer transformers, none of which is needed for Dartium. But if you were to load the app in Chrome/FF you need all of them to run. Pub-serve is meant to support both, so we can't just choose to run them or not run them depending on whether we are in pub-serve or pub-build.
We could try to optimize out transformers to be faster, but the bottom line is that the best optimization is not to run them altogether :-).
It would be great to have support for this in pub-serve/barback.