These two classes have a lot of duplicated code for no reason.

Bug: angleproject:5563
Change-Id: Ia9d8efeb50f3e52ffb1df6a6e462efdb20fd4a9a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2636678
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Peng Huang <penghuang@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>