code: private void setTypeRequested(ResourceType type) {
      synchronized (typeToFirstWait) {
        if (!typeToFirstWait.containsKey(type)) {
          typeToFirstWait.put(type, null);
        }
      }
    }
docs: Set the resource type to requested for first wait metrics.  The value will
  be set to null to denote the difference between waiting and requested and
  not waiting.
  
  @param type Resource type that is will be set to requested for metrics.