Gets and sets properties of an extension's sidebar.
A sidebar is a pane that is displayed at the left-hand or right-hand side of the browser window, next to the web page. The browser provides a UI that enables the user to see the currently available sidebars and to select a sidebar to display. Using the sidebar_action manifest.json key, an extension can define its own sidebar. Using the sidebarAction API described here, an extension can get and set the sidebar's properties.
The sidebarAction API is closely modeled on the browserAction API.
The sidebarAction API is based on Opera's sidebarAction API. However, note that the following are not yet supported: setBadgeText(), getBadgeText(), setBadgeBackgroundColor(), getBadgeBackgroundColor(), onFocus, onBlur.