Now clean up damage on all fragments that belong to a Flow. This ensures
that damage does not re-propagate up to the parent Flow from the
Fragments. It also means that the flow tree dump should show a more
accurate picture of the state of the flow tree.
Source-Repo: https://github.com/servo/servo
Source-Revision: 1436ee5afab4ede68ab834c7d6368a7d45ede7ac