Method declareExtension

src/service/ampdoc-impl.js:425–433

* Adds a declared extension to an ampdoc. * @param {string} extensionId * @param {string} version * @restricted

(extensionId, version)

   * @restricted
   */
  declareExtension(extensionId, version) {
    devAssert(
      !this.declaredExtensions_[extensionId] ||
        this.declaredExtensions_[extensionId] === version,
      'extension already declared %s',
      extensionId
    );
    this.declaredExtensions_[extensionId] = version;
  }

  /**
   * @param {string} extensionId