Panels are windows that are visible to the user even while the user is interacting with other applications. The small windows are positioned at the bottom of the screen, with minimal manual window management by the user. This API will allow extension developers to create and use panels.
An extension opens small "pop up" windows, for example, separate chat sessions, calculator, media player, stock/sport/news ticker, task list, scratchpad, that the user wants to keep visible while using a different application or browsing a different web site. Scattered "pop up" windows are difficult for the user to keep track of, therefore panels are placed along the bottom of the screen and are "always on top".
The user would like easy control of chat windows: finding them, moving them out of the way, etc. Window management of separate chat "pop ups" is time consuming. All panels can be minimized/maximized together.
Could this API be part of the web platform?
Eventually, yes. The current needs are from extension developers. If we figure out how to make this work in the wider context of web platform, we will propose it for the web platform at that point.
Do you expect this API to be fairly stable?
What UI does this API expose?
Panels will be a new type of window with some unique behaviors and UI.
How could this API be abused?
An extension could open an excessive number of panels, repeatedly open and close panels, or unnecessarily draw the user's attention to a panel.
How would you implement your desired features if this API didn't exist?
Extensions could continue to use "pop up" windows and let users manually arrange them on their screen such that they will not be obscured by other applications. Users would manage each "pop up" individually.
Are you willing and able to develop and maintain this API?
Extend the chrome.windows.* API to add a new "panel" type, as Panels are simply another type of window.
chrome.windows.create with type="panel" will create a new Panel window. Unlike other window types, Panels do not take focus by default. The focused attribute can be used to change the default behavior.
chrome.windows.update has a new drawAttention option to attract the user's attention to a Panel. This API can be used for all window types. The behavior to attract the user's attention will vary depending on window type and OS.
All other actions on the panel can be achieved via manipulations on the DOMWindow or the window contents, e.g. change the size of the div containing all window content to resize the panel.
Panels are regular windows as far as other extensions [that did not create the panel] are concerned and are included in all other windows-related API, e.g. chrome.windows.getAll, chrome.extensions.getViews.