Vulkan backend render targets don't allow client to specify stencil bits

We already always create the stencil buffer even for wrapped RTs.

Make VulkanWindowContext use SkSurface::MakeFromBackendRenderTarget.

Change-Id: I5df429d347331801954ec17cb9d75e323a7af345
Reviewed-on: https://skia-review.googlesource.com/113206
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/vk/GrVkGpu.cpp b/src/gpu/vk/GrVkGpu.cpp
index b674185..1acbf02 100644
--- a/src/gpu/vk/GrVkGpu.cpp
+++ b/src/gpu/vk/GrVkGpu.cpp
@@ -942,11 +942,13 @@
     desc.fSampleCnt = 1;
 
     sk_sp<GrVkRenderTarget> tgt = GrVkRenderTarget::MakeWrappedRenderTarget(this, desc, info);
-    if (tgt && backendRT.stencilBits()) {
-        if (!createStencilAttachmentForRenderTarget(tgt.get(), desc.fWidth, desc.fHeight)) {
-            return nullptr;
-        }
+
+    // We don't allow the client to supply a premade stencil buffer. We always create one if needed.
+    SkASSERT(!backendRT.stencilBits());
+    if (tgt) {
+        SkASSERT(tgt->canAttemptStencilAttachment());
     }
+
     return tgt;
 }