Add aggregate transformer types to barback.

This doesn't make the types public yet. However, it does run non-aggregate
transformers using AggregateTransform.

R=rnystrom@google.com
BUG=18567

Review URL: https://codereview.chromium.org//262173009

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@35864 260f80e4-7a28-3924-810f-c04153c831b5
11 files changed
tree: c949dc5bd6559c4504941d3eabad97aac13d08bb
  1. example/
  2. lib/
  3. test/
  4. CHANGELOG.md
  5. LICENSE
  6. pubspec.yaml
  7. README.md
README.md

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.