There is a HashMap in ScrollingCoordinatorMac that maps ScrollingNodeIDs to ScrollingStateNodes. The nodes themselves should keep track of this ID. Then the id can be used to make sure ScrollingStateNodes remove themselves from the HashMap when they are destroyed, and it will also be useful for associating ScrollingStateNodes with ScrollingTreeNodes over on the scrolling thread.
Created attachment 168473 [details] Patch
Attachment 168473 [details] did not pass style-queue: Failed to run "['Tools/Scripts/check-webkit-style', '--diff-files', u'Source/WebCore/ChangeLog', u'Source/WebCor..." exit_code: 1 Source/WebCore/page/scrolling/ScrollingStateNode.h:31: Alphabetical sorting problem. [build/include_order] [4] Total errors found: 1 in 6 files If any of these errors are false positives, please file a bug against check-webkit-style.
Created attachment 168474 [details] Patch
Thanks, Simon! Committed change: http://trac.webkit.org/changeset/131221