Use whenComplete so the condition runs even in error case.

Review URL: https://chromiumcodereview.appspot.com//12181020
Fixes for next sdk

Review URL: https://chromiumcodereview.appspot.com//12181004
Print unit in the output of perf.dart

Review URL: https://chromiumcodereview.appspot.com//12186027
Add sdk dependency to pubspec

Review URL: https://chromiumcodereview.appspot.com//12208015
include revision in sdk constraint
Replace mappedBy with map (mappedBy will be removed in the future).

Review URL: https://chromiumcodereview.appspot.com//12221034
Fix web-ui to use source_maps spans.

Review URL: https://chromiumcodereview.appspot.com//12210053
Update CHANGELOG.md
Update the webui dartium extension

Review URL: https://chromiumcodereview.appspot.com//12221076
fix #318 - use web-ui-dev@dartlang.org list

This new list is for discussing development of web-ui
add a note about the web-ui-dev list
add web-ui-dev to code review settings

Review URL: https://chromiumcodereview.appspot.com//12213096