Roll src/third_party/skia 139e88015cb5..df2726ee7a36 (2 commits)

https://skia.googlesource.com/skia.git/+log/139e88015cb5..df2726ee7a36

git log 139e88015cb5..df2726ee7a36 --date=short --no-merges --format='%ad %ae %s'
2019-10-08 jcgregorio@google.com Revert "Another attempt to fix vpython in Cloud Build."
2019-10-08 robertphillips@google.com Add GrRenderTask and GrOp prePrepare framework

Created with:
  gclient setdep -r src/third_party/skia@df2726ee7a36

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 kjlubick@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/+/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
TBR=kjlubick@google.com

Bug: chromium:993053
Change-Id: Ic60725d041f89df912fb4562ba8e2922339aa849
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1848544Reviewed-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@{#704030}

DEPS

@@ -167,7 +167,7 @@ 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': '139e88015cb50eb24cb6f1df585e443e4377beea',
+  'skia_revision': 'df2726ee7a36f0de3ab3d1303f3742ed1ac35740',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.