mac: Don't set background color from a frame until frame is displayed

content/browser/renderer_host/render_widget_host_view_mac.h

Index: content/browser/renderer_host/render_widget_host_view_mac.h
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.h b/content/browser/renderer_host/render_widget_host_view_mac.h
index 3c7f8501fe8a8747dec418be451a49c9f74f64fd..78376e1b376f1bb9ada5de3849bf12e60cac0c0d 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.h
+++ b/content/browser/renderer_host/render_widget_host_view_mac.h
@@ -556,6 +556,7 @@ class CONTENT_EXPORT RenderWidgetHostViewMac
   // The background color of the web content. This color will be drawn when the
   // web content is not able to draw in time.
   SkColor background_color_ = SK_ColorTRANSPARENT;
+  SkColor last_frame_root_background_color_ = SK_ColorTRANSPARENT;
 
   // Factory used to safely scope delayed calls to ShutdownHost().
   base::WeakPtrFactory<RenderWidgetHostViewMac> weak_factory_;