Use Offscreen Surface for Split Screen

tools/viewer/sk_app/WindowContext.h

Index: tools/viewer/sk_app/WindowContext.h
diff --git a/tools/viewer/sk_app/WindowContext.h b/tools/viewer/sk_app/WindowContext.h
index fdd847445c25df03d250f10d96f34fe71c03b5fe..b6718875123c175ca52fd2048779fe63f4e112c4 100644
--- a/tools/viewer/sk_app/WindowContext.h
+++ b/tools/viewer/sk_app/WindowContext.h
@@ -44,7 +44,8 @@ public:
     virtual GrBackendContext getBackendContext() = 0;
     GrContext* getGrContext() const { return fContext; }
 
-    sk_sp<SkSurface> createRenderSurface(sk_sp<GrRenderTarget>, int colorBits);
+    sk_sp<SkSurface> createRenderSurface(
+            sk_sp<GrRenderTarget>, int colorBits, bool offscreen = false, bool sRGB = false);

[djsollen, 2016/06/16 16:55:05]

As a public API I don't like this and think it tries to combine 2 different
functions because their implementation is similar not because they are intended
to be used the same way.

I propose a new function something like

sk_sp<SkSurface> createOffscreenSurface(...)

This function can share a common private implementation with the existing
function.

     void presentRenderSurface(sk_sp<SkSurface> renderSurface, sk_sp<GrRenderTarget> rt,
                               int colorBits);