Roll src/third_party/skia/ f12d84275..255607f09 (2 commits)

https://skia.googlesource.com/skia.git/+log/f12d84275cfa..255607f094da

$ git log f12d84275..255607f09 --date=short --no-merges --format='%ad %ae %s'
2017-08-02 mtklein 8-bit hacking
2017-08-02 skia-deps-roller Roll skia/third_party/externals/angle2/ 6c58b0620..a0bcc50be (2 commits)

Created with:
  roll-dep src/third_party/skia
BUG=750813


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=liyuqian@chromium.org

Change-Id: I93ac33e9029b8ae6540dc545d28b4d53c986890b
Reviewed-on: https://chromium-review.googlesource.com/598511Reviewed-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@{#491634}

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': 'f12d84275cfaff4b140694e33313a3581955abf8',
+  'skia_revision': '255607f094dac0f1c075a5b718005e7bd4d03e3d',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.