In https://bugs.webkit.org/show_bug.cgi?id=207858, the WebGL conformance
test conformance/glsl/misc/shader-struct-scope.html was failing. The
workaround that fixes this test was enabled only on desktop GL, but it's
necessary for iOS as well.

Bug: angleproject:4642
Change-Id: I29b96f16dd0608bb9597a4a9903e375a64dadf3d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2207636Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: James Darpinian <jdarpinian@chromium.org>