getStringValue() {
    switch (this.type) {
      case IDENTIFIER_EXPRESSION:
      case BINDING_IDENTIFIER:
        return this.identifierToken.toString();
      case IMPORTED_BINDING:
        return this.binding.getStringValue();
      case PROPERTY_NAME_SHORTHAND:
        return this.name.toString();
      case LITERAL_PROPERTY_NAME:
        return this.literalToken.toString();
    }

    throw new Error('Not yet implemented');

  }
Gets the string value of a tree. This matches the StringValue static
semantics of the spec.
@returns {string}