Tighten up SkSpecialSurface factory functions

This is split out of https://codereview.chromium.org/1930013002/ ((Mostly) Retract GrRenderTarget from SkGpuDevice)

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1925313002

Review-Url: https://codereview.chromium.org/1925313002
diff --git a/tests/ImageFilterTest.cpp b/tests/ImageFilterTest.cpp
index 54e9a60..56b3aaf 100644
--- a/tests/ImageFilterTest.cpp
+++ b/tests/ImageFilterTest.cpp
@@ -370,12 +370,9 @@
 static sk_sp<SkSpecialSurface> create_empty_special_surface(GrContext* context, int widthHeight) {
 #if SK_SUPPORT_GPU
     if (context) {
-        GrSurfaceDesc desc;
-        desc.fConfig = kSkia8888_GrPixelConfig;
-        desc.fFlags  = kRenderTarget_GrSurfaceFlag;
-        desc.fWidth  = widthHeight;
-        desc.fHeight = widthHeight;
-        return SkSpecialSurface::MakeRenderTarget(context, desc);
+        return SkSpecialSurface::MakeRenderTarget(context,
+                                                  widthHeight, widthHeight,
+                                                  kSkia8888_GrPixelConfig);
     } else
 #endif
     {