Aura-Mus: Enable Surface Synchronization behind flag

ui/compositor/layer.h

Index: ui/compositor/layer.h
diff --git a/ui/compositor/layer.h b/ui/compositor/layer.h
index ac7a176477724fa5f758c299bd15fcd074a67e8d..bbb0962ef3416242b09fde04b4143a91a0dea430 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -299,6 +299,10 @@ class COMPOSITOR_EXPORT Layer
       const cc::SurfaceInfo& surface_info,
       scoped_refptr<cc::SurfaceReferenceFactory> surface_ref);
 
+  // In the event that the primary surface is not yet available in the
+  // display compositor, the fallback surface will be used.
+  void SetFallbackSurface(const cc::SurfaceInfo& surface_info);
+
   bool has_external_content() {
     return texture_layer_.get() || surface_layer_.get();
   }