来自官方:
How to disable Device Mode
Device Mode is enabled by default. If you’re building a Desktop-only site, you may turn it off by pressing the Toggle device mode (toggle device mode icon on) icon. When Device Mode is disabled, the icon turns grey and the viewport controls are hidden.
You can also toggle device mode on and off using the keyboard shortcut: Ctrl+Shift+M (or Cmd+Shift+M on Mac). To use this shortcut your mouse needs to be focused on your DevTools window. If it’s focused on your viewport, you’ll trigger Chrome’s switch user shortcut.
Remember
Device Mode does a whole lot to give you an experience as close as possible compared to the real deal, but keep in mind that you'll still need to test on real devices to get the full picture (we can't yet emulate the performance characteristics of a real device).
https://developers.google.com/web/tools/chrome-devtools/iterate/device-mode/
大意就是整合到一起了。