Bug 1476368 - Pre-allocate vectors in HitTester::read_clip_scroll_tree. r=kvark
Bug 1476368 - Pre-allocate vectors in HitTester::read_clip_scroll_tree. r=kvark

Differential Revision: https://phabricator.services.mozilla.com/D20507

[wrupdater] From https://hg.mozilla.org/mozilla-central/rev/b512bb5087969ce96190d48bd2488a81b580beb9

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