Couple of WebGL and ANGLE tests with Metal backend broken by #1696

See http://crbug.com/1227129

conformance/glsl/misc/ternary-operators-in-initializers.html WebGL test was broken when running on top of ANGLE's Metal backend.
As well as StateChangeTestES3.SamplerMetadataUpdateOnSetProgram/ES3_Metal in angle_end2end_tests.

Example failures:
https://ci.chromium.org/ui/p/chromium/builders/try/mac_optional_gpu_tests_rel/62223/overview

@HansKristian-Work

Start with crbug.com/1227129 and the cited Chromium try build, then inspect conformance/glsl/misc/ternary-operators-in-initializers.html and StateChangeTestES3.SamplerMetadataUpdateOnSetProgram/ES3_Metal. Reproduce the failures on ANGLE's Metal backend and use both named tests to confirm they pass without regressions.

Written by the indexing model from the issue text.