Bug 1414961 - enable WR dual-source blending by default. r=jrmuizel
Bug 1414961 - enable WR dual-source blending by default. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D30107

[wrupdater] From https://hg.mozilla.org/mozilla-central/rev/52da0d93fe09c1bf8ed98f3e690b258ca80661ec

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