Chrome Version       : 59.0.3071.125
URLs (if applicable) : https://www.w3schools.com

What steps will reproduce the problem?
1. Visit https://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_win_settimeout
   : https://www.w3schools.com > JAVASCRIPT > JS Browser BOM > JS Timing > The setTimeout() Method > Try it Yourself
2. Click 'Try it' button and send Chrome to background
   : Push device's home button to send it background simply
3. Wait a few seconds


What is the expected result?
Chrome browser should stay on background. 
And the javascript popup may be shown when user relaunch Chrome browser explicitly.


What happens instead?
Chrome browser comes back to foreground with javascript popup automatically.


Please provide any additional information below. Attach a screenshot if
possible.
Reproducing ratio : 100%
 
Actually, the reproducing step is just test page to help understand this situation.
I can see some commercial web sites do act like this, which I feel a little bit inconvenient.
For example, you can see this situation like this in real world.
1. Turn on 'Restrict Background data' for Chrome
2. Visit https://m.naver.com and push home button while loading or right after loading finished
3. Do anything you want except for Chrome browsing
4. Chrome comes back to foreground with JS popup in 10~15 seconds

Query : Why Chrome browser makes itself foreground state when javascript popup is emitted after browser goes background?
Is there any special reason not to stay background?