To turn on GC instrumentation, define JS_GCMETER.
- To turn on GC mark-phase debugging, useful to find leaked objects by their address, and to dump the GC heap, define GC_MARK_DEBUG. See the code in jsgc.c around the declaration and use of js_LiveThingToFind.
- To turn on the arena package′s instrumentation, define JS_ARENAMETER.
- To turn on the hash table package′s metering, define JS_HASHMETER

