Add support for querying GL_MAX_VARYING_COMPONENTS. BUG=angle:645 Change-Id: I2e33798bd7fe6cabb1237224aeb9e59cdf03f73c Reviewed-on: https://chromium-review.googlesource.com/198836 Reviewed-by: Nicolas Capens <nicolascapens@chromium.org> Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>