Remove invariant declaration in vertex shader for translation from ESSL 3.00 to GLSL <= 4.1 This is a follow-up patch of https://chromium-review.googlesource.com/408569. This CL removes invariant declaration in ESSL 3.00 vertex shader, such like: " out vec4 foo; invariant foo; " This CL also adds the workarounds in libANGLE. BUG=chromium:639760 TEST=webgl2_conformance Change-Id: I568ab51a9a2f5da10d1aff0b63aae8805097e081 Reviewed-on: https://chromium-review.googlesource.com/409157 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>