* Add default
* Convert function to non-static
* Remove static for private functions
* Replace .call
* Move functions with side effects into a synchronous prepare function
* Rename variables with "container" to "frame" in _initializeFrame
* Rename variables with "container" to "frame"
* Rename getContainer to getFrame
* Rename getContainerRect to getFrameRect
* Organize and simplify
* Fix incorrect change of "popup" => "this"
* Move initial _updateVisibility into prepare()
* Rename PopupProxyHost to PopupFactory
* Update FrontendApiReceiver to support non-async handlers
* Make some functions non-async
* Make setCustomCss non-async
* Make setContentScale non-async
* Remove static
* Rename variables
* Pass frameId into PopupFactory's constructor
* Change FrontendApiReceiver source from popup-proxy-host to popup-factor
* Rename _invokeHostApi to _invoke
* Rename PopupProxy.getHostUrl to getUrl
