Expose aggregate transformers in barback. R=rnystrom@google.com BUG=18567 Review URL: https://codereview.chromium.org//299833003 git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@36777 260f80e4-7a28-3924-810f-c04153c831b5
Barback is an asset build system. It is the library underlying pub's asset transformers in pub build and pub serve.
Given a set of input files and a set of transformations (think compilers, preprocessors and the like), it will automatically apply the appropriate transforms and generate output files. When inputs are modified, it automatically runs the transforms that are affected.
To learn more, see here.