refactor/cleanup dart completion cache

BUG=
R=scheglov@google.com

Review URL: https://codereview.chromium.org//816233002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42556 260f80e4-7a28-3924-810f-c04153c831b5
Add DEPS for sunflower. Used by dart2js tests.

Review URL: https://codereview.chromium.org//819173003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42557 260f80e4-7a28-3924-810f-c04153c831b5