function setUseSeparateIncognitoSettings(value) {
  if (!value) {
    pref.clear({'incognito': true});
  } else {
    // Explicitly set the value for incognito mode.
    pref.get({'incognito': true}, function(settings) {
      pref.set({'incognito': true, 'value': settings.value});
    });
  }
  document.getElementById('incognitoValue').disabled = !value;
}
Called from the UI to change whether to use separate settings for
incognito mode.

@param value{boolean} whether to use separate settings for
incognito mode.