To create a web app within ChromeOS from an existing web page, access the URL in question as normal. Click on the three button overflow menu selection –> More Tools –> Add to shelf.
A small dialog box should appear. You can rename the entry and also use the available option to open the shortcut within a new window.
A new shortcut icon should appear on the taskbar.
To remove the “Open as window” option, right-click on the taskbar icon and uncheck the menu selection.