Roll Skia from 4b9b34558fe5 to 7b9da25e1b8b (11 revisions)

https://skia.googlesource.com/skia.git/+log/4b9b34558fe5..7b9da25e1b8b

2020-08-03 ethannicholas@google.com Can now swizzle SkSL scalars
2020-08-03 jvanverth@google.com Revise GrMtlGpu::onUpdateBackendTexture.
2020-08-03 herb@google.com add chrome bug triage to the Sheriff's Documentation
2020-08-03 herb@google.com move source padding to the AtlasLocator
2020-08-03 brianosman@google.com Always send premul paint color to shader FPs
2020-08-03 johnstiles@google.com Enable ClangTidy check modernize-make-unique.
2020-08-03 jvanverth@google.com Fix texture errors on iOS Metal
2020-08-03 reed@google.com Add arc methods to path builder
2020-08-03 jvanverth@google.com Remove unused dynamic allocation code from GrMtlResourceProvider.
2020-08-03 cwallez@chromium.org GN: Add support for GN's framework variable in the toolchain
2020-08-03 johnstiles@google.com Increase ClangTidy code coverage by enabling features.

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 herb@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: herb@google.com
Change-Id: I7e86849b892cceaa00bf1930970d8603c34a41fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2335562Reviewed-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@{#794252}

DEPS

@@ -195,7 +195,7 @@ 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': '4b9b34558fe544e4abffa55128c2d94cdd2f34ce',
+  'skia_revision': '7b9da25e1b8b893a063879908ac9eba9323868d0',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.