We disable shader cache for Validating decoder in chrome, so port this
workaround into ANGLE to see if it can fix crbug.com/1203652.

Bug: chromium:1203652,chromium:480992
Change-Id: I08611c148217abc9c32d11fefe8a7d15873f3b30
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2867269
Commit-Queue: Peng Huang <penghuang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>