The following dEQP cases can pass with
https://chromium-review.googlesource.com/c/1207216:

dEQP-GLES31.functional.texture.gather.basic.2d_array.rgba8.texture_swizzle.*
dEQP-GLES31.functional.texture.gather.offset.implementation_offset.2d_array.rgba8.texture_swizzle.*

Bug: angleproject:2826
Test: dEQP-GLES31.functional.texture.gather.basic.2d_array.rgba8.texture_swizzle.*
      dEQP-GLES31.functional.texture.gather.offset.implementation_offset.2d_array.rgba8.texture_swizzle.*

Change-Id: Iaf6c4ca5abff1a7ae97d47a0d323bead38a7d8c1
Reviewed-on: https://chromium-review.googlesource.com/c/1267659Reviewed-by: Jiajia Qin <jiajia.qin@intel.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>