Use Offscreen Surface for Split Screen

tools/viewer/sk_app/Window.cpp

Index: tools/viewer/sk_app/Window.cpp
diff --git a/tools/viewer/sk_app/Window.cpp b/tools/viewer/sk_app/Window.cpp
index 7ec8baae36b7ef04f5ae0f92b17711e066568fd0..dfc5c2e453c582acbfb2e1a6ce06b3bef09e7c6d 100644
--- a/tools/viewer/sk_app/Window.cpp
+++ b/tools/viewer/sk_app/Window.cpp
@@ -7,6 +7,7 @@
 
 #include "Window.h"
 
+#include "GrRenderTarget.h"
 #include "SkSurface.h"
 #include "SkCanvas.h"
 #include "VulkanWindowContext.h"
@@ -113,4 +114,8 @@ void Window::markInvalProcessed() {
     fIsContentInvalidated = false;
 }
 
+sk_sp<SkSurface> Window::getOffscreenSurface(bool sRGB) {
+    return fWindowContext->createRenderSurface(nullptr, 0, true, sRGB);
+}
+
 }   // namespace sk_app