Bug 1612941 - properly detect GL_ARB_texture_swizzle extension in WR. r=gw,kvark
Bug 1612941 - properly detect GL_ARB_texture_swizzle extension in WR. r=gw,kvark

Differential Revision: https://phabricator.services.mozilla.com/D65596

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/3cae17a5ec80e4ee12fe173a414fcd5eb46f9a41

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