Ref GrDirectContext in MakeBackendRenderTargetSurface

Fixes crashes when running vkbert config where we tear down a Vulkan
GrDirectContext before deleting the backing store of a SkSurface
created via MakeBackendRenderTargetSurface.

Bug: skia:10843
Change-Id: I99ea2266ba14325d3aaac5ee59aa712688fb9329
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/327196
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
1 file changed