function flattenSingleChildIntoContext(traverseContext, child, name) {
  // We found a component instance.
  var result = traverseContext;
  var keyUnique = result[name] === undefined;
  if ("development" !== 'production') {
    "development" !== 'production' ? warning(keyUnique, 'flattenChildren(...): Encountered two children with the same key, ' + '`%s`. Child keys must be unique; when two children share a key, only ' + 'the first child will be used.', name) : undefined;
  }
  if (keyUnique && child != null) {
    result[name] = child;
  }
}
@param {function} traverseContext Context passed through traversal.
@param {?ReactComponent} child React child component.
@param {!string} name String name of key path to child.