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. Reland of: https://chromium-review.googlesource.com/#/c/287570 BUG=angleproject:1102 TEST=angle_unittest Change-Id: I064d918d65f37539cb1e14f12173ca5591a4ea3f Reviewed-on: https://chromium-review.googlesource.com/301711Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>
