Method whenExtensionsKnown

src/service/ampdoc-impl.js:455–457

* Resolved when the initial document set of extension is known. * @return {!Promise}

()

   * @return {!Promise}
   */
  whenExtensionsKnown() {
    return this.signals_.whenSignal(AmpDocSignals_Enum.EXTENSIONS_KNOWN);
  }

  /**
   * Returns the root node for this ampdoc. It will either be a `Document` for