Roll external/skia 610842af9..6ecc91107 (4 commits)

https://skia.googlesource.com/skia.git/+log/610842af9..6ecc91107

2017-06-16 egdaniel@google.com Revert "Revert "Remove Gr*Gpu includes from header files.""
2017-06-16 bsalomon@google.com Remove GrRectOpFactory::MakeAAFillWithDevRect
2017-06-16 bsalomon@google.com Rename GrDrawOp::xpRequiresDstTexture to finalize and change return type to an enum
2017-06-16 egdaniel@google.com Revert "Revert "Add API for flushing surfaces with gpu semaphores""

Test: Presubmit checks will test this change.
Change-Id: I51f8dd73f2df4fadda4a9393184537a78be141a5