Roll external/skia 11f898f15..5af44defb (1 commits)

https://skia.googlesource.com/skia.git/+log/11f898f15..5af44defb

2017-07-19 robertphillips@google.com Add GrResourceAllocator class + unit test

Test: Presubmit checks will test this change.
Change-Id: I3425ae445d9f4b70372af49d309bf9377109d905