Roll src/third_party/skia c2d84bfa7421..9c173c8347f8 (2 commits)

https://skia.googlesource.com/skia.git/+log/c2d84bfa7421..9c173c8347f8

git log c2d84bfa7421..9c173c8347f8 --date=short --no-merges --format='%ad %ae %s'
2019-09-09 brianosman@google.com Remove temporary Metal pipeline cache size hack
2019-09-09 hcm@google.com Add release section for milestones and rel notes

Created with:
  gclient setdep -r src/third_party/skia@9c173c8347f8

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 mtklein@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=mtklein@google.com

Bug: None
Change-Id: I594b7d02d39a67c5401e9c3071264313e4646fa4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1792237Reviewed-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@{#694962}

DEPS

@@ -162,7 +162,7 @@ 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': 'c2d84bfa74212bf97405429225b88944d1377c69',
+  'skia_revision': '9c173c8347f877f6d889ba328f206b2f7e409fbf',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.