Don't store resources with a unique key in GrResourceCache's fScratchMap

The reasoning here is that resources with a unique key are never selected from fScratchMap and just clog up the search for an available resource.

This knocks a 200x loop over the SVGbouncingrects case from 264ms down to 164ms.

BUG=603969
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2008083002

Review-Url: https://codereview.chromium.org/2008083002
2 files changed