For SCALARIZE_VEC_AND_MAT_CONSTRUCTOR_ARGS, assign precision to temp variables. Otherwise on Windows or other platforms with GLES backend, using this workaround will trigger shader compile failure. For the moment, to simplify the workaround, for any missing precisions in float, we always assign the highest available precion to it. BUG=angle:695 TEST=webgl conformance tests Change-Id: I810579442bc7fc61d6a52b76aff31a779046fa22 Reviewed-on: https://chromium-review.googlesource.com/211253 Tested-by: Zhenyao Mo <zmo@chromium.org> Reviewed-by: Kenneth Russell <kbr@chromium.org>