Last round of effect->processor (for now)

R=joshualitt@google.com

Review URL: https://codereview.chromium.org/659803005
Prefer to recycle non-RT scratch textures that don't have pending IO

BUG=skia:2889

Review URL: https://codereview.chromium.org/650283002
Make GrFragmentProcessor auto-compare coord xforms.

Review URL: https://codereview.chromium.org/657923002