Roll src/third_party/skia/ cecd617a4..21cc9950c (6 commits).

https://chromium.googlesource.com/skia.git/+log/cecd617a4297..21cc9950c4b4

$ git log cecd617a4..21cc9950c --date=short --no-merges --format='%ad %ae %s'
2016-09-13 mikejurka re-add SkDebug_stdio for Fuchsia builds
2016-09-13 bungeman Simulated fonts aren't TrueType fonts.
2016-09-13 fmalita [SVGDom] Linear gradient 'gradientTransform' support
2016-09-13 mtklein Update gn_android_flavor for Vulkan.
2016-09-13 jcgregorio No \n in bench names.
2016-09-13 mtklein Android GN: don't reboot before running

BUG=639198

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel
TBR=djsollen@google.com

Review-Url: https://codereview.chromium.org/2336233003
Cr-Commit-Position: refs/heads/master@{#418442}

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': 'cecd617a4297ffdcec632ca7e2ed1e6b61665e04',
+  'skia_revision': '21cc9950c4b4eb183c315c7d417e36342a9f1cf9',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.