Allow stencils to be attached to render targets created via SkSurface::MakeFromBackendTextureAsRenderTarget

This is a regression from "Refactor to separate backend object lifecycle
and GpuResource budget decision".

GrGLRenderer::canAttemptStencilAttachment was incorrectly returning false
for all wrapped render targets. This function should return false only if
the FBO is wrapped (unowned). If the FBO is owned by Skia, we can attach
stencils.

BUG=608238

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1924183003

Review-Url: https://codereview.chromium.org/1941353003
2 files changed