SkPicture::cullRect is a virtual method called from DrawingDisplayItem::Raster:
https://cs.chromium.org/chromium/src/cc/playback/drawing_display_item.cc?q=DrawingDisplayItem::Raster&sq=package:chromium&l=82&dr=CSs

Its implementations are actually trivial, and can be potentially turned into a short switch statement:

SkRect SkBigPicture::cullRect() const override { return fCullRect; }
SkRect SkEmptyPicture::cullRect() const override { return SkRect::MakeEmpty(); }
SkRect SkMiniPicture::cullRect() const override { return fCull; }

This can be turned into something like (pseudo-code):

switch(typeof(picture_)) {
case SkBigPicture: static_cast<SkBigPicture*>(picture_)->fCullRect; 
case SkEmptyPicture: SkRect::MakeEmpty();
case SkMiniPicture: static_cast<SkMiniPicture*>(picture_)->fCull;
}

This looks like something that can be done automatically (and be worth it), but we need to find more places before we can justify spending time on implementing such optimization.