Bug 1594128 - Work around Mac GLSL compiler bug. r=kvark
Bug 1594128 - Work around Mac GLSL compiler bug. r=kvark

The GLSL compiler appears to get confused by a function that just returns a defined constant.
See https://github.com/servo/webrender/wiki/Driver-issues#bug-1594128---glsl-on-macos-is-confused-by-a-function-that-just-returns-a-constant

Differential Revision: https://phabricator.services.mozilla.com/D54691

[wrupdater] From https://hg.mozilla.org/mozilla-central/rev/39f51911efa8fc0969cd32fd0c4f2ef5d1651ae5

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