chore: Convert IAbortableOperation to ES6 (#7623)

Author: tykus160

externs/shaka/abortable.js

@@ -18,39 +18,39 @@
  * @template T
  * @exportDoc
  */
-shaka.extern.IAbortableOperation = function() {};
-
-
-/**
- * A Promise which represents the underlying operation.  It is resolved when
- * the operation is complete, and rejected if the operation fails or is
- * aborted.  Aborted operations should be rejected with a shaka.util.Error
- * object using the error code OPERATION_ABORTED.
- *
- * @const {!Promise.<T>}
- * @exportDoc
- */
-shaka.extern.IAbortableOperation.prototype.promise;
-
-
-/**
- * Can be called by anyone holding this object to abort the underlying
- * operation.  This is not cancelation, and will not necessarily result in
- * any work being undone.  abort() should return a Promise which is resolved
- * when the underlying operation has been aborted.  The returned Promise
- * should never be rejected.
- *
- * @return {!Promise}
- * @exportDoc
- */
-shaka.extern.IAbortableOperation.prototype.abort = function() {};
-
-
-/**
- * @param {function(boolean)} onFinal A callback to be invoked after the
- *   operation succeeds or fails.  The boolean argument is true if the operation
- *   succeeded and false if it failed.
- * @return {!shaka.extern.IAbortableOperation.<T>} Returns this.
- * @exportDoc
- */
-shaka.extern.IAbortableOperation.prototype.finally = function(onFinal) {};
+shaka.extern.IAbortableOperation = class {
+  constructor() {
+    /**
+     * A Promise which represents the underlying operation.  It is resolved when
+     * the operation is complete, and rejected if the operation fails or is
+     * aborted.  Aborted operations should be rejected with a shaka.util.Error
+     * object using the error code OPERATION_ABORTED.
+     *
+     * @const {!Promise.<T>}
+     * @exportDoc
+     */
+    this.promise;
+  }
+
+  /**
+   * Can be called by anyone holding this object to abort the underlying
+   * operation.  This is not cancelation, and will not necessarily result in
+   * any work being undone.  abort() should return a Promise which is resolved
+   * when the underlying operation has been aborted.  The returned Promise
+   * should never be rejected.
+   *
+   * @return {!Promise}
+   * @exportDoc
+   */
+  abort() {}
+
+
+  /**
+   * @param {function(boolean)} onFinal A callback to be invoked after the
+   *   operation succeeds or fails.  The boolean argument is true
+   *   if the operation succeeded and false if it failed.
+   * @return {!shaka.extern.IAbortableOperation.<T>} Returns this.
+   * @exportDoc
+   */
+  finally(onFinal) {}
+};