mus: Fix showing guest views in --mash and --mus.

ui/aura/window_delegate.h

Index: ui/aura/window_delegate.h
diff --git a/ui/aura/window_delegate.h b/ui/aura/window_delegate.h
index 644c0cee287fd8ca7607c77c833352ac24202113..c463cf88605406df8524ab7f5086efcbce4b37b0 100644
--- a/ui/aura/window_delegate.h
+++ b/ui/aura/window_delegate.h
@@ -12,6 +12,10 @@
 #include "ui/events/event_handler.h"
 #include "ui/gfx/native_widget_types.h"
 
+namespace cc {
+class SurfaceInfo;
+}
+
 namespace gfx {
 class Path;
 class Point;
@@ -94,6 +98,8 @@ class AURA_EXPORT WindowDelegate : public ui::EventHandler {
   // above returns true.
   virtual void GetHitTestMask(gfx::Path* mask) const = 0;
 
+  virtual void OnWindowSurfaceChanged(const cc::SurfaceInfo& surface_info) {}
+
  protected:
   ~WindowDelegate() override {}
 };