Chrome Version       : 55.0.2883.95
URLs (if applicable) :
Other browsers tested:
  Add OK or FAIL, along with the version, after other browsers where you
have tested this issue:
     Safari: n/a
    Firefox: n/a
         IE: n/a

What steps will reproduce the problem?
(1) Configure proxy to require login on Mac or Chromebook
(2) Open a new tab in Chrome browser so that proxy authentication dialog box opens up
(3) Reload an extension or wait for an extension that is polling to make a request and witness dialog box disappear

What is the expected result?
The dialog box should not disappear just because an extension makes a request in the background.

What happens instead?
The dialog box disappears and if an extension is polling frequently, it may be impossible to authenticate with the proxy

Please provide any additional information below. Attach a screenshot if
possible.
Here is a quickCast of the behavior: http://quick.as/oz9Xur66b