generate new message details page and fix logic for injecting {%raw} tags only when making messages for the website

R=sigmund@google.com

Review URL: https://codereview.chromium.org//780813003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42133 260f80e4-7a28-3924-810f-c04153c831b5