DEPS.xwalk: Roll ozone-wayland (39d93a6 -> a4e3e96).

a4e3e96 Build Fix.
282d501 Backport parts of 08cd65ef and 7f2153f3.
5c7b2cd OzoneDisplay: Remove logic in DefaultDisplaySpec

This includes changes required to allow oz-wl to build with compilers that
support the `override' keyword, as well as a build fix for Tizen IVI/Generic
due to sign warnings turned errors.