Revert "Fix Viewer slide load on backend change"

This reverts commit 5fb009df3c87167762b33483ee82b5fe632837a9.

Reason for revert: Broke first slide.

Original change's description:
> Fix Viewer slide load on backend change
> 
> Currently Viewer fires unbalanced load events on backend change.
> 
> Instead of calling setupCurrentSlide() with an invalid prevSlide and
> always forcing a slide load, pass a |force| argument on backend change.
> 
> Change-Id: I146b42331f5aa9721d4f407b81c13f4512d67d61
> Reviewed-on: https://skia-review.googlesource.com/94960
> Reviewed-by: Brian Osman <brianosman@google.com>
> Commit-Queue: Florin Malita <fmalita@chromium.org>

TBR=brianosman@google.com,fmalita@chromium.org

Change-Id: I52bbc9fb44f6ed4e04bcc549b2ec72c8600c823a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/94861
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>
2 files changed