Makes it an error to access gl_FragDepthEXT in #version 300 es shader. TODO: Lacks the feature to make "#extension GL_EXT_frag_depth : require" an error for #version 300 es. BUG=angleproject:1102 TEST=angle_unittest Change-Id: Ic313a0e1ed6369550d53885290f300fab1aaf304 Reviewed-on: https://chromium-review.googlesource.com/287570Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Zhenyao Mo <zmo@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>
