Scaffolding for testing incremental compilation.

R=johnniwinther@google.com

Review URL: https://codereview.chromium.org//645513002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41070 260f80e4-7a28-3924-810f-c04153c831b5
Mark test as flaky on Safari

R=ricow@google.com

Review URL: https://codereview.chromium.org//652583003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41071 260f80e4-7a28-3924-810f-c04153c831b5
Firefox is slow

Review URL: https://codereview.chromium.org//650113002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41072 260f80e4-7a28-3924-810f-c04153c831b5