After making layers with contents layers have pink borders, we can see from http://www.webkit.org/blog-files/3d-transforms/poster-circle.html that we're making color contents layers for lots of things now, but setting a transparent color on them.
RenderLayerBacking::updateDirectlyCompositedBackgroundColor() is getting rendererBackgroundColor(), which returns a valid (but transparent) color.
At least for TextureMapper this is not a problem, I'm not familiar with the implications of this for CA.
Do you avoid contentsLayers for the transparent color?
Content layers are really more of a CA concept... In TextureMapper we just mark those layers as having a solid color and no backing store and they're rendered that way.
But in general it should be safe to treat "transparent" solid color as a sign to delete the content layer, as an optimization inside GraphicsLayerCA and friends.
Created attachment 216343 [details]
Comment on attachment 216343 [details]
View in context: https://bugs.webkit.org/attachment.cgi?id=216343&action=review
> + Fix only making a background-color layer if the color is not transparent (zero alpha).
fix only making.