Roll external/skia 96555343063b..76eef9a21f84 (3 commits)

https://skia.googlesource.com/skia.git/+log/96555343063b..76eef9a21f84

2019-08-05 fmalita@chromium.org Add missing GrLumaColorFilterEffect opt flag
2019-08-05 michaelludwig@google.com Update tests to use new image filter factories
2019-08-05 michaelludwig@google.com Fix GMs broken during API porting

The AutoRoll server is located here: https://skia-autoroll.corp.goog/r/android-master-autoroll

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.

Test: Presubmit checks will test this change.
Change-Id: I2d5c1d3ff777cf0855bfc9828d6d26e5d219caf2
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.