It causes incorrect compilation of some shaders. The original graphics
driver bugs that motivated enabling it have been fixed, at least on
one of the platforms (macOS).

Tested with new WebGL conformance test in
https://github.com/KhronosGroup/WebGL/pull/3214 .

Bug: chromium:1165751
Change-Id: Iee9747769ca918aab143592d6cf158ce02a75ee0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2661024
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>