remove extension, fixes #534

R=sigmund@google.com

Review URL: https://chromiumcodereview.appspot.com//17096007
hide linked list: dart:collections now have a LinkedList.

R=jmesserly@google.com

Review URL: https://chromiumcodereview.appspot.com//17230005
publish 0.4.12 - breaking changes for 0.5.20
fix rendertest: we moved smart string matcher to unittest

Review URL: https://chromiumcodereview.appspot.com//17332002
fix #540 - update the sourcemap url

R=gram@google.com

Review URL: https://chromiumcodereview.appspot.com//17315014
bump spec
Merge branch 'master' of https://github.com/dart-lang/web-ui into breaking_change
cleanup for all tests to run
cleanup