Bug 1578569 - Restore padding-bottom on certain menupopups inside BMB_bookmarksPopup r=mak

This was removed in Bug 1573158, where the following line change forced it to 0px:
https://hg.mozilla.org/integration/autoland/rev/3f54e52c52eb#l2.12

This uses shadow parts instead of Shadow DOM + XBL selectors into the arrowscrollbox,
which unblocks arrowscrollbox Custom Element conversion and appears to have the same
visual effect as far as I can tell.

Differential Revision: https://phabricator.services.mozilla.com/D44556

--HG--
extra : moz-landing-system : lando

browser/base/content/browser.xhtml

@@ -1302,6 +1302,7 @@
             <menupopup id="BMB_bookmarksToolbarPopup"
                        is="places-popup"
                        placespopup="true"
+                       nofooterpopup="true"
                        context="placesContext"
                        onpopupshowing="if (!this.parentNode._placesView)
                                          new PlacesMenu(event, `place:parent=${PlacesUtils.bookmarks.toolbarGuid}`,
@@ -1322,6 +1323,7 @@
             <menupopup id="BMB_unsortedBookmarksPopup"
                        is="places-popup"
                        placespopup="true"
+                       nofooterpopup="true"
                        context="placesContext"
                        onpopupshowing="if (!this.parentNode._placesView)
                                          new PlacesMenu(event, `place:parent=${PlacesUtils.bookmarks.unfiledGuid}`,
@@ -1335,6 +1337,7 @@
             <menupopup id="BMB_mobileBookmarksPopup"
                        is="places-popup"
                        placespopup="true"
+                       nofooterpopup="true"
                        context="placesContext"
                        onpopupshowing="if (!this.parentNode._placesView)
                                          new PlacesMenu(event, `place:parent=${PlacesUtils.bookmarks.mobileGuid}`,

browser/components/places/content/browserPlacesViews.js

@@ -715,9 +715,9 @@ PlacesViewBase.prototype = {
     }
 
     if (!hasMultipleURIs) {
-      aPopup.setAttribute("singleitempopup", "true");
+      aPopup.setAttribute("nofooterpopup", "true");
     } else {
-      aPopup.removeAttribute("singleitempopup");
+      aPopup.removeAttribute("nofooterpopup");
     }
 
     if (!hasMultipleURIs) {

browser/themes/shared/customizableui/panelUI.inc.css

@@ -242,6 +242,10 @@ panelview {
   padding-bottom: 0px;
 }
 
+#BMB_bookmarksPopup menupopup[nofooterpopup=true]::part(popupbox) {
+  padding-bottom: 4px;
+}
+
 #confirmation-hint {
   --arrowpanel-background: #0060df;
   --arrowpanel-border-color: #0060df;