This simplifies reference management and make the swapchain's reentrant
code avoid APIEntryPoints.
Bug: dawn:723
Change-Id: I6c456b9ec349c73d783dbb12a284f322d0be4e1a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/84763
Reviewed-by: Loko Kung <lokokung@google.com>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>