LayerTreeCoordinatorProxy can be used after calling LayerTreeCoordinatorProxy::purgeBackingStores(). So we should clear cached ShareableSurfaces.
Created attachment 171323 [details] Patch
Comment on attachment 171323 [details] Patch Clearing flags on attachment: 171323 Committed r132861: <http://trac.webkit.org/changeset/132861>
All reviewed patches have been landed. Closing bug.