This fixes the WebGL test glsl_misc_struct_equals as well as
several dEQP tests in functional.shaders.struct.

BUG=391957
BUG=angle:910

Change-Id: I09f3cd3f51bbc3541b64dbcfddfe01884ddba6f5
Reviewed-on: https://chromium-review.googlesource.com/247083Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>