Roll src/third_party/skia/ 2790c52e3..bbab477b4 (1 commit).

https://skia.googlesource.com/skia.git/+log/2790c52e36dd..bbab477b49e2

$ git log 2790c52e3..bbab477b4 --date=short --no-merges --format='%ad %ae %s'
2016-12-08 jvanverth Add documentation for Viewer

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=msarett@google.com

Review-Url: https://codereview.chromium.org/2570433003
Cr-Commit-Position: refs/heads/master@{#437824}

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': '2790c52e36ddd8c46d8238f3c92f47779f79fb69',
+  'skia_revision': 'bbab477b49e2aed0f257206ce457814c953d574b',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.