Roll src/third_party/skia/ db90e26e2..85ff84821 (1 commit).

https://skia.googlesource.com/skia.git/+log/db90e26e2bb7..85ff84821d5f

$ git log db90e26e2..85ff84821 --date=short --no-merges --format='%ad %ae %s'
2016-12-29 reed remove unused ForceUnique option from makeImageSnapshot

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
TBR=liyuqian@google.com

Review-Url: https://codereview.chromium.org/2607153002
Cr-Commit-Position: refs/heads/master@{#440969}

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': 'db90e26e2bb7f0bf767e04129673bd2fa48545a6',
+  'skia_revision': '85ff84821d5f6c8d48f2af12bdffdd3b5f8baf2c',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.