While working on the DevTools profiler, I've noticed that durations are sometimes incorrect. This seems to be vaguely related to high/low priority state updates. Need to track this down more so I'm filing an issue for myself.
state = {};
        render() {
          instance = this;
          return this.props.children;
        }
      }
      class Pure extends React.PureComponent {
        render() {
          return this.props.children;
        }
      }
      const renderer = ReactTestRenderer.create(
        <React.unstable_Profiler id="outer" onRender={callback}>
          <Updater>
            <React.unstable_Profiler id="middle" onRender={callback}>
              <Pure>
                <React.unstable_Profiler id="inner" onRender={callback}>
                  <div />
                </React.unstable_Profiler>
              </Pure>
            </React.unstable_Profiler>
          </Updater>