Roll src/third_party/skia/ cc0937273..aa840647f (4 commits).

https://chromium.googlesource.com/skia.git/+log/cc0937273030..aa840647fc7f

$ git log cc0937273..aa840647f --date=short --no-merges --format='%ad %ae %s'
2016-09-23 bsalomon Don't compute path keys for volatile paths in GrShape.
2016-09-23 csmartdalton Add Pixel C knobs to skpbench
2016-09-23 jvanverth Some Vulkan memory fixes and cleanup
2016-09-23 reed change SkXfermodeImageFilter to carry no impl information

BUG=649562

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

Review-Url: https://codereview.chromium.org/2367933002
Cr-Commit-Position: refs/heads/master@{#420710}

DEPS

@@ -39,7 +39,7 @@ 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': 'cc09372730301be78b9d26c1198db1584622cdd9',
+  'skia_revision': 'aa840647fc7f057715bce62489b96c4299385135',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.