Fix lazy coding in ViaSingletonPictures.

Fix lazy coding in ViaSingletonPictures.

I was using SkRect::MakeLargest() as bounds, which is sort of nutso,
as that clearly is way out of bounds for how big a picture can feasibly
be, i.e. something closer to SkIRect::MakeLargest().

This was causing spurious quick rejects in drawPatch().  I didn't really
look much deeper to figure out why.  It's easy enough to just feed it the
proper bounds of the entire content.

This means patch_primitive draws correctly in sp-8888 mode.
I also noticed the GM was too small... it clipped off most of its content.
So I've made it larger.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1865143002

Review URL: https://codereview.chromium.org/1865143002