When the FrameView has a non-opaque background color, make sure the TileCache tiles are not opaque
https://bugs.webkit.org/show_bug.cgi?id=107989

Reviewed by Dean Jackson.

If a WKView was told to draw a transparent background, make sure that we
set the TileCache tiles to be non-opaque.

* rendering/RenderLayerBacking.cpp:
(WebCore::RenderLayerBacking::updateRootLayerConfiguration):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@140873 268f45cc-cd09-0410-ab3c-d52691b4dbfc