Yesterday I landed support for a way to dump and inspect a GC heap snapshot. This work was motivated by the need to have easier ways to debug Document leaks, especially those involving GC.

The basic idea is that you do some steps that trigger a document leak, then get a heap dump. Typically this involves loading the test page, then navigating away, clearing caches, triggering a GC and capturing a snapshot. The snapshot is dumped as JSON file in /tmp; you can then drag this snapshot into the view which lives in Tools/GCHeapInspector, and see why objects are referencing the leaked document.

This is documented on https://trac.webkit.org/wiki/Inspecting%20the%20GC%20heap 

Let me know if you have questions. Improvements to the inspector page are welcomed.

Simon