This change adds constant folding support for following built-ins: - atan(two arguments), pow, mod, mix, step and smoothstep. BUG=angleproject:913 TEST=dEQP tests Following 80 tests from dEQP-GLES3.functional.shaders.constant_expressions started passing with this change: - builtin_functions.angle_and_trigonometry.atan_separate* - builtin_functions.exponential.pow_* - builtin_functions.common.mod_* - builtin_functions.common.mix_* - builtin_functions.common.step_* - builtin_functions.common.smoothstep_* Change-Id: I70f0a8837a82c480da8cff3f1382c6252a486fe4 Reviewed-on: https://chromium-review.googlesource.com/271753Reviewed-by: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org> Tested-by: Olli Etuaho <oetuaho@nvidia.com>
