Work around abs() issue in Intel Mac drivers abs(i) where i is an integer returns unexpected result in Intel Mac. This works around the issue by emulating abs(i) manually. BUG=chromium:642227 TEST=deqp/functional/gles3/shadercommonfunction.html Change-Id: I2a41e0f4bcb0766109d651e663283b1760468017 Reviewed-on: https://chromium-review.googlesource.com/377628 Commit-Queue: Zhenyao Mo <zmo@chromium.org> Reviewed-by: Zhenyao Mo <zmo@chromium.org>