Roll Skia from cdff3fcba638 to 960bd2dbaa6a (4 revisions)

https://skia.googlesource.com/skia.git/+log/cdff3fcba638..960bd2dbaa6a

2020-12-21 mtklein@google.com allow arbitrary Builder Features
2020-12-21 brianosman@google.com SkSL: In the front-end, rename PipelineStage to RuntimeEffect
2020-12-21 rmistry@google.com Update go.skia.org/infra in go.mod/go.sum
2020-12-21 bsalomon@google.com compare kernel in GrBicubicEffect

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/skia-autoroll
Please CC bungeman@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/master/autoroll/README.md

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux-blink-rel;luci.chromium.try:linux-chromeos-compile-dbg;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Cq-Do-Not-Cancel-Tryjobs: true
Bug: None
Tbr: bungeman@google.com
Change-Id: Iddbd56b825422c30996b495f59bc6702abc0a5c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2599919Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#838747}

DEPS

@@ -199,7 +199,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling Skia
   # and whatever else without interference from each other.
-  'skia_revision': 'cdff3fcba6384563c48465f06eb10d48ab77e5b3',
+  'skia_revision': '960bd2dbaa6a2130330c5f693e2a07a24aeca392',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.