Roll src/third_party/skia/ 59ad782b2..18f960209 (4 commits)

https://skia.googlesource.com/skia.git/+log/59ad782b2b05..18f9602094ac

$ git log 59ad782b2..18f960209 --date=short --no-merges --format='%ad %ae %s'
2017-05-04 egdaniel Add support for Geom shaders in Vulkan backend.
2017-05-04 herb Factor out common code from sweep and linear.
2017-05-04 jvanverth Add ShadowUtils sample.
2017-05-04 benjaminwagner Marker for Windows NVIDIA driver update.

Created with:
  roll-dep src/third_party/skia


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

If the roll is causing failures, see:
http://www.chromium.org/developers/tree-sheriffs/sheriff-details-chromium#TOC-Failures-due-to-DEPS-rolls


CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel
TBR=scroggo@chromium.org

Change-Id: Ide81efd89d01095d7389948976ed2b95afbb2722
Reviewed-on: https://chromium-review.googlesource.com/496546Reviewed-by: Skia Deps Roller <skia-deps-roller@chromium.org>
Commit-Queue: Skia Deps Roller <skia-deps-roller@chromium.org>
Cr-Commit-Position: refs/heads/master@{#469466}

DEPS

@@ -40,7 +40,7 @@ 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': '59ad782b2b05b07aa6eb961aa4d62e934093cbd1',
+  'skia_revision': '18f9602094ace030cf73fa389bab555bc1e21b1f',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.