Bug 1561305. Eliminate unused viewport_tiles field. r=nical
Bug 1561305. Eliminate unused viewport_tiles field. r=nical

Differential Revision: https://phabricator.services.mozilla.com/D35807

[wrupdater] From https://hg.mozilla.org/mozilla-central/rev/1e3513e5290b6927d3f34474c29c65d9718ad4c7

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender