Changes for SDK 0.4.6

Review URL: https://chromiumcodereview.appspot.com//13985028
Fix html5lib for latest SDK changes

Review URL: https://chromiumcodereview.appspot.com//14265018
release version 0.4.3
Cleanup html5lib dependencies

Review URL: https://chromiumcodereview.appspot.com//14294012
update test/run.sh to use the new analyzer
switch to content_shell in html5lib tests

Review URL: https://chromiumcodereview.appspot.com//16398013
Fixes for latest SDK
removed uses of deprecated dart:io Path class
Merge pull request #70 from kevmoo/master

Updates for latest SDK
fix pubspec.yaml