function handleMemoryEvent(subject, topic, json) {
  if (topic != 'garbage-collection-statistics') {
    return;
  }

  // Broadcast the event to all active workers.
  // We avoid parsing it here and let the pages handle it.
  for each (injectedTab in injectedTabs) {
    injectedTab.queueDebuggerRecord(['gc', json]);
  }
}
Handler for memory observation events.
@param {*} subject Anything.
@param {string} topic Event name.
@param {[type]} json JSON string of GC data.