Work around unpackHalf2x16 emulation for Intel Mac Negative operator is buggy in an expression on Intel Mac. Use abs(v) to replace -v for negative value. BUG=chromium:644057 TEST=deqp/functional/gles3/shaderpackingfunction.html Change-Id: I6182e7a00b162e36ed9278c0e5a2fdd8fb480959 Reviewed-on: https://chromium-review.googlesource.com/381152 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>