Roll src/third_party/skia/ b5dc4051f..81681949d (3 commits).

https://chromium.googlesource.com/skia.git/+log/b5dc4051f722..81681949d363

$ git log b5dc4051f..81681949d --date=short --no-merges --format='%ad %ae %s'
2016-07-21 caryclark allow curves on side of lines to be very small
2016-07-21 borenet Add "skp" asset
2016-07-21 vjiaoblack Creating framework for drawShadowedPicture GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2146073003

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_blink_rel
TBR=jcgregorio@google.com

Review-Url: https://codereview.chromium.org/2168653006
Cr-Commit-Position: refs/heads/master@{#406928}

DEPS

@@ -36,7 +36,7 @@ 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': 'b5dc4051f722d9c65d55eb3a65e0e8d031e107ad',
+  'skia_revision': '81681949d363f777809af167c70912ca2a612036',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.