Make sk_app::WindowContext directly create a SkSurface without an intermediate GrRenderTarget

tools/viewer/sk_app/GLWindowContext.cpp

Index: tools/viewer/sk_app/GLWindowContext.cpp
diff --git a/tools/viewer/sk_app/GLWindowContext.cpp b/tools/viewer/sk_app/GLWindowContext.cpp
index b960da4824d06eb3f3309f8907948ed40bceaaaf..31ba01c292a3229ebdbd72c60cf38188680f095f 100644
--- a/tools/viewer/sk_app/GLWindowContext.cpp
+++ b/tools/viewer/sk_app/GLWindowContext.cpp
@@ -83,9 +83,8 @@ sk_sp<SkSurface> GLWindowContext::getBackbufferSurface() {
             GrGLint buffer;
             GR_GL_CALL(fBackendContext, GetIntegerv(GR_GL_FRAMEBUFFER_BINDING, &buffer));
             desc.fRenderTargetHandle = buffer;
-            fRenderTarget.reset(fContext->textureProvider()->wrapBackendRenderTarget(desc));
 
-            fSurface = this->createRenderSurface(fRenderTarget, fActualColorBits);
+            fSurface = this->createRenderSurface(desc, fActualColorBits);
         }
     }