WindowSurfaceCGL: unregister the SwapLayer on destruction Previously the SwapLayer was kept in the CALayer hierarchy after WindowSurfaceCGL's destruction which caused SwapLayer's callbacks to be called after the shared data was freed, causing a segfault. BUG=angleproject:1233 Change-Id: I71dce45330e6b7d5f06a41198c10890b1d8d520e Reviewed-on: https://chromium-review.googlesource.com/320711 Tryjob-Request: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Corentin Wallez <cwallez@chromium.org>