docs: function instrument(component, callback, context) {
      var instrumentName, val, details, end;
      // Only instrument if there's at least one subscriber.
      if (_emberMetalInstrumentation.subscribers.length) {
        if (component) {
          instrumentName = component.instrumentName;
        } else {
          instrumentName = 'node';
        }
        details = {};
        if (component) {
          component.instrumentDetails(details);
        }
        end = _emberMetalInstrumentation._instrumentStart('render.' + instrumentName, function viewInstrumentDetails() {
          return details;
        });
        val = callback.call(context);
        if (end) {
          end();
        }
        return val;
      } else {
        return callback.call(context);
      }
    }