The unstabe-features configuration option was introduced so the build-webkit script usage could force enabling the unstable features (i.e. features under development, unstable features). The build-webkit script now does Some Other Magic (TM) to get that done, so this feature should be disabled.
There are some usages of the Automake variable tied to this configure option that require a small amount of attention to remove them properly, but otherwise this is straightforward.
Created attachment 180289 [details]
Created attachment 180296 [details]
Comment on attachment 180296 [details]
Clearing flags on attachment: 180296
Committed r138252: <http://trac.webkit.org/changeset/138252>
All reviewed patches have been landed. Closing bug.