This fixes an omission that out parameter tracking had inherited from EmulatePrecision. Accurate tracking of when values are written is required for converting dynamic indexing of vectors and matrices to function calls. A new test covering this is added to angle_unittests. TEST=angle_unittests BUG=angleproject:1116 Change-Id: I05c5fd60355117d0053b84110748ae221375a790 Reviewed-on: https://chromium-review.googlesource.com/290562Reviewed-by: Zhenyao Mo <zmo@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Olli Etuaho <oetuaho@nvidia.com>
