Clean up test drawContext usage

gm/bigrrectaaeffect.cpp

Index: gm/bigrrectaaeffect.cpp
diff --git a/gm/bigrrectaaeffect.cpp b/gm/bigrrectaaeffect.cpp
index b8529618264676778a3603a589e63c8164f0268f..b3f39a0f2db0df09102bcd3105207e93455773a0 100644
--- a/gm/bigrrectaaeffect.cpp
+++ b/gm/bigrrectaaeffect.cpp
@@ -49,15 +49,9 @@ protected:
     SkISize onISize() override { return SkISize::Make(fWidth, fHeight); }
 
     void onDraw(SkCanvas* canvas) override {
-        GrRenderTarget* rt = canvas->internal_private_accessTopLayerRenderTarget();
-        GrContext* context = rt ? rt->getContext() : nullptr;
-        if (!context) {
-            skiagm::GM::DrawGpuOnlyMessage(canvas);
-            return;
-        }
-
-        sk_sp<GrDrawContext> drawContext(context->drawContext(sk_ref_sp(rt)));
+        GrDrawContext* drawContext = canvas->internal_private_accessTopLayerDrawContext();
         if (!drawContext) {
+            skiagm::GM::DrawGpuOnlyMessage(canvas);
             return;
         }
 
@@ -90,7 +84,7 @@ protected:
                 SkASSERT(fp);
                 if (fp) {
                     pipelineBuilder.addCoverageFragmentProcessor(fp);
-                    pipelineBuilder.setRenderTarget(rt);
+                    pipelineBuilder.setRenderTarget(drawContext->accessRenderTarget());
 
                     SkRect bounds = testBounds;
                     bounds.offset(SkIntToScalar(x), SkIntToScalar(y));