Roll src/third_party/skia/ aa840647f..d68f9b003 (3 commits).

https://chromium.googlesource.com/skia.git/+log/aa840647fc7f..d68f9b00389b

$ git log aa840647f..d68f9b003 --date=short --no-merges --format='%ad %ae %s'
2016-09-23 mtklein GN: ANGLE
2016-09-23 brianosman Change SkSpecialImage::makeSurface and makeTightSurface to take output properties (color space), bounds, and (optional) alphaType.
2016-09-23 robertphillips Add validation of RRects to SkValidatingReadBuffer

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

Review-Url: https://codereview.chromium.org/2367103002
Cr-Commit-Position: refs/heads/master@{#420775}

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': 'aa840647fc7f057715bce62489b96c4299385135',
+  'skia_revision': 'd68f9b00389bf676b171f250e684486cb2fbd404',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.