Defer more renderTargetContexts in the GPU image filter paths

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4767

Change-Id: I4c1f27247ef340a49d1ac96761810e77e6047ca2
Reviewed-on: https://skia-review.googlesource.com/4767
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
8 files changed