Roll external/skia a8825f5a8..f9ad5ba8f (5 commits)

https://skia.googlesource.com/skia.git/+log/a8825f5a8..f9ad5ba8f

2019-07-29 mtklein@google.com don't try to format removed files
2019-07-29 ethannicholas@google.com renamed SkSL texture() and process() to sample()
2019-07-29 jvanverth@google.com Use shared mode for Metal texture upload buffers.
2019-07-29 brianosman@google.com Allow defined functions in the SkSL .inc files
2019-07-29 csmartdalton@google.com skpbench: invoke 'adb wait-for-device' lazily

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: Ic3f933099166257d6e3e428385385ede31a2aa87
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.