Add HTML test with two dart scripts on one page.

BUG=dartbug.com/20698
R=sigurdm@google.com

Review URL: https://codereview.chromium.org//732533002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41794 260f80e4-7a28-3924-810f-c04153c831b5