Fix a bug where barback transformers would produce stale output. For the gory details, see the new test in pkg/barback/test/package_graph/transform/concurrency_test.dart. R=rnystrom@google.com BUG=19038 Review URL: https://codereview.chromium.org//306773002 git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@36780 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.