Make sk_app::WindowContext directly create a SkSurface without an intermediate GrRenderTarget
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2165703002

Review-Url: https://codereview.chromium.org/2165703002
diff --git a/tools/viewer/sk_app/WindowContext.h b/tools/viewer/sk_app/WindowContext.h
index 2c526a4..917eb4e 100644
--- a/tools/viewer/sk_app/WindowContext.h
+++ b/tools/viewer/sk_app/WindowContext.h
@@ -45,13 +45,14 @@
     GrContext* getGrContext() const { return fContext; }
 
     sk_sp<SkSurface> createOffscreenSurface(bool sRGB);
-    sk_sp<SkSurface> createRenderSurface(sk_sp<GrRenderTarget>, int colorBits);
     void presentRenderSurface(sk_sp<SkSurface> renderSurface, sk_sp<GrRenderTarget> rt,
                               int colorBits);
 
 protected:
     virtual bool isGpuContext() { return true;  }
 
+    sk_sp<SkSurface> createRenderSurface(GrBackendRenderTargetDesc, int colorBits);
+
     GrContext*        fContext;
 
     int               fWidth;
@@ -62,7 +63,7 @@
 
 private:
     sk_sp<SkSurface> createSurface(
-            sk_sp<GrRenderTarget>, int colorBits, bool offscreen, bool forceSRGB);
+            GrBackendRenderTargetDesc*, int colorBits, bool offscreen, bool forceSRGB);
 };
 
 }   // namespace sk_app