Implement aura::WindowPortMus::CreateCompositorFrameSink()

ui/aura/mus/mus_context_factory.h

Index: ui/aura/mus/mus_context_factory.h
diff --git a/ui/aura/mus/mus_context_factory.h b/ui/aura/mus/mus_context_factory.h
index 11b2065e90fad78626094050fc10714f776a5cfd..444ae37cae9e599b79c81b2bf22525b78e0be662 100644
--- a/ui/aura/mus/mus_context_factory.h
+++ b/ui/aura/mus/mus_context_factory.h
@@ -10,6 +10,7 @@
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
+#include "cc/output/context_provider.h"
 #include "cc/surfaces/surface_manager.h"
 #include "services/ui/public/cpp/raster_thread_helper.h"
 #include "services/ui/public/interfaces/window_tree.mojom.h"
@@ -56,6 +57,8 @@ class AURA_EXPORT MusContextFactory : public ui::ContextFactory {
 
   ui::RasterThreadHelper raster_thread_helper_;
   ui::Gpu* gpu_;
+  scoped_refptr<cc::ContextProvider> shared_main_thread_context_provider_;
+
   base::WeakPtrFactory<MusContextFactory> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MusContextFactory);