This is an essential extension. I have no idea how this basic functionally could be removed from Chrome. It is up to individual websites to warn if the user is about to leave whiteout saving first. That covers backspace, back button in browser, forward button in browser, back button on mouse, forward button on mouse, links, closing the browser, closing the tab etc. Removing a key feature because some sites are broken is stupid!
Restores browser behavior of navigating to previous page when pressing the Backspace key
Requires permissions to inject code in all pages visited
Can be installed from source for security verification