Roll src/third_party/skia/ 51494f661..ac568a934 (6 commits)

https://skia.googlesource.com/skia.git/+log/51494f6615b8..ac568a934f8f

$ git log 51494f661..ac568a934 --date=short --no-merges --format='%ad %ae %s'
2018-01-25 mtklein 1010102, 101010x, 888x in sw
2018-01-30 reed saturate some irect ops for fuzzers
2018-01-30 halcanary SkQP: fix upload/download scripts
2018-01-30 bsalomon Fix mock tex rt gpu mem size
2018-01-30 angle-skia-autoroll Roll skia/third_party/externals/angle2/ 513bc77df..bd6ae4aa1 (1 commit)
2018-01-30 jvanverth Revert "Reduce the amount of padding needed for SDFs, take 2"

Created with:
  roll-dep src/third_party/skia


The AutoRoll server is located here: https://autoroll.skia.org

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

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.


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
TBR=bungeman@chromium.org

Change-Id: I93cdd6392681b0a670aba84f2c260f4a08519c1b
Reviewed-on: https://chromium-review.googlesource.com/894172Reviewed-by: skia-chromium-autoroll <skia-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Commit-Queue: skia-chromium-autoroll <skia-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#533138}

DEPS

@@ -79,7 +79,7 @@ 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': '51494f6615b8bd637caf0fd6d0d577ea19d50948',
+  'skia_revision': 'ac568a934f8f82bf3a359b757d67eb3a797d3593',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.