Changes

Setting the <code>XPC_SHUTDOWN_HEAP_DUMP</code> environment variable to a file name will cause XPConnect to, at shutdown, dump a log to that file explaining why all remaining JS objects are still alive. This may be sufficient to debug some JS-related leaks without the full rebuild required by DEBUG_CC. It also shows more information about reachability, since it shows property names for all connections.

The cycle collector heap dump is useful for figuring out why the cycle collector is keeping an object alive. These can either be manually or automatically generated. They can be generated in both debug and non-debug builds.