Google has removed support for panels in Chrome 54 on all platforms except on Chrome OS. Panels, which were only enabled on developer versions of Chrome by default, and had to be enabled on other versions using the enable panels flag on chrome://flags, looked like notifications on first glance.
They enabled extension developers to spawn windows on the screen that one could best describe as advanced notification windows.
The main advantages that panels offered in comparison were that they supported custom sizes, could be minimized or moved, supported always on top functionality, and allowed for custom HTML and CSS code.
Google removes Panel support from Chrome
Google removed Panel support from Google Chrome in version 54. If you set the enable panels flag previously you will notice that it is not there anymore when you open the about:flags page.
Also, any extension that relied on panels for its functionality won't be able to do so anymore. This means that some extensions will stop working altogether -- if all their functionality is triggered by opening a panel -- or some functionality won't work anymore if panels were used to power some features of the extension.
Popular extensions, Google's own Hangouts extensions or Trello for Chrome, made use of panels.
You are probably wondering why Google removed the functionality. One of Google's engineers gives the following explanation for the removal.
Panels on non-chromeos were an experimental feature and only supported on Dev channel, or on other channels behind a flag.
They are costly to maintain and we were never happy with their stability and functionality on Windows, Mac and Linux. As a result we've removed them.
We understand this will be annoying for users of extensions that rely on them, but this is part of an alignment of Chrome as being fundamentally a web browser supporting web applications.
The original developer of Panels for Chrome added the following statement.
The time passes and things change, we all learn. In case of Panels, we "proved" by practice that it takes a team of a few engineers full time to be able to catch up with teams of OS developers in Windows, OSX, Linux and even our own ChromeOS. The window management and graphics/input subsystems are constantly evolving and it is more or less prohibitively expensive for a small team to try to build and keep a high quality but non-standard window management mode.
OSes have too many mechanisms that are linked to a specific windows behaviors (focus, window switching, active windows treatment, titlebars, where input goes, shortcuts, animations, multiple desktops, other OS gadgets etc), and usually OSes do not provide 'hooks' or APIs to integrate with those, which makes it necessary to 'reverse-engineer' and hack around. While it can be done, it quickly leads to 'card house' design that falls down even easier with the next major OS update
Basically, it is too expensive to maintain panels functionality, and stability and functionality never met Google's expectations either.
Now You: Are you affected by the removal of Panels support in Google Chrome?