With pub build and pub serve the same transformer can be run on the same asset in parallel. We want to maintain the cache between the runs, so making the resolver pipeline these requests.
In addition, refactoring to dramatically change the role of ResolverTransformer- previously it was a transformer that automatically kept the AST up to date, but this does not work well when in a pipeline of transformers that are generating or modifying code. What was ResolverTransformer is Resolvers- a cache of resolvers for which individual transformers now need to request the resolver from.
ResolverTransformer is now a mixin which can be used to automatically release a Resolver when it's done being used.
BUG=
R=sigmund@google.com
Review URL: https://codereview.chromium.org//181383015
git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@33163 260f80e4-7a28-3924-810f-c04153c831b5
blois@google.com