EmulatePrecision: Round constructor args only when needed Constructor arguments don't need to be rounded if the constructor result will be rounded to the same precision. This will make precision emulated shaders slightly faster to execute in some cases. BUG=angleproject:874 TEST=angle_unittests Change-Id: I4220cd2289c97dcf5b7a25a4cbdd18487947c2d2 Reviewed-on: https://chromium-review.googlesource.com/500288 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>