Following https://bugs.webkit.org/show_bug.cgi?id=158686, it seems that Shadow DOM can be enabled on all platforms and that corresponding build flag can be removed (a runtime flag is available).
Created attachment 281264 [details] Patch
Comment on attachment 281264 [details] Patch Rejecting attachment 281264 [details] from commit-queue. Failed to run "['/Volumes/Data/EWS/WebKit/Tools/Scripts/webkit-patch', '--status-host=webkit-queues.webkit.org', '--bot-id=webkit-cq-03', 'apply-attachment', '--no-update', '--non-interactive', 281264, '--port=mac']" exit_code: 2 cwd: /Volumes/Data/EWS/WebKit Last 500 characters of output: tching file Source/cmake/tools/vsprops/FeatureDefines.props patching file Source/cmake/tools/vsprops/FeatureDefinesCairo.props patching file Tools/ChangeLog Hunk #1 succeeded at 1 with fuzz 3. patching file Tools/Scripts/webkitperl/FeatureList.pm patching file Tools/TestWebKitAPI/Configurations/FeatureDefines.xcconfig patching file ChangeLog Failed to run "[u'/Volumes/Data/EWS/WebKit/Tools/Scripts/svn-apply', '--force', '--reviewer', u'Ryosuke Niwa']" exit_code: 1 cwd: /Volumes/Data/EWS/WebKit Full output: http://webkit-queues.webkit.org/results/1505932
Created attachment 281352 [details] Patch
Comment on attachment 281352 [details] Patch Same patch after a rebase
Comment on attachment 281352 [details] Patch Clearing flags on attachment: 281352 Committed r202091: <http://trac.webkit.org/changeset/202091>
All reviewed patches have been landed. Closing bug.