merge_pr_26
[css-break] Implement
fragmentation.Differential Revision: https://phabricator.services.mozilla.com/D53709
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=471015
gecko-commit: 2684fdcd6fbff5abe54a3e1c018e7188abb4076c
gecko-integration-branch: autoland
gecko-reviewers: TYLin