Refactors support for toggle control flags, --enable-toggles= &
--disable-toggles, from the end2end tests into a utility class to make
them available elsewhere. The unittests now uses this utility class to
parse toggle control flags.
For some toggles, like 'use_tint_generator', the unittests are known to
be broken with them turned on. They will be fixed in subsequent CLs.
BUG=dawn:756
Change-Id: Ic283e8a82bedcbf255258cca3e62f58c79d3857b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/47740
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
