Clean up Program::validate. This method should really be an Impl method, since it corresponds to a specific OpenGL call. Making it an Impl method also allows us to remove applyUniforms, which doesn't correspond to a GL call. BUG=angleproject:1123 Change-Id: I2abee3cfaa7393cad44566782d51ed701e84846b Reviewed-on: https://chromium-review.googlesource.com/293825 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>