Click the vertical ellipsis button ( ⋮ ) then choose the desired docking option. (the docking option with the red circle around it, is undock)
For older version of Chrome, press and hold the corner button
You can also undock/dock-to-left/dock-to-right/dock-to-bottom from the Command Menu. Press Cmd+Shift+P (Mac) or Cmd+Shift+P (Windows, Linux, Chrome OS) to open the Command Menu, then start typing bottom/left/right/undock.
DevTools documentation on docking: https://developers.google.com/web/tools/chrome-devtools/ui#placement