Support multiview in ESSL 1.00 shaders Support is added according to the proposal for WEBGL_multiview. When the multiview extension is enabled in an ESSL 1.00 shader, num_views can be specified using a layout qualifier. To support this, enabling the multiview extension makes "layout" a keyword rather than an identifier in ESSL 1.00. The type of gl_ViewID_OVR is also different in case of ESSL 1.00: it has to be a signed integer, since unsigned integers are not supported in ESSL 1.00. Some existing tests for multiview shaders are extended in this patch. The changes make sure that vertex shader "in" qualifier is still allowed in ESSL 3.00 multiview shaders, since this patch adds code to disallow it in ESSL 1.00 multiview shaders. BUG=angleproject:1669 TEST=angle_unittests Change-Id: I65dbbbebabdb24cf0bb647d40aa80cebf713c4f7 Reviewed-on: https://chromium-review.googlesource.com/506088 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>