use shared code transformer, update web_components to remove .map and .concat files

This is a redo of https://codereview.chromium.org/540633002/ because I had deleted my local branch and didn't know how to recover it.

Review URL: https://codereview.chromium.org//724723003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41724 260f80e4-7a28-3924-810f-c04153c831b5