Still missing from this patch: HLSL output, implicitly sized arrays.

Tested with WebGL 2 test sdk/tests/deqp/data/gles3/shaders/arrays.html

TEST=WebGL 2 conformance tests
BUG=angleproject:941

Change-Id: I900f2af843fd8046f23dd4b77352e77026bbba84
Reviewed-on: https://chromium-review.googlesource.com/265652Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>