[menus] All menu in files-ng shall have margin-top: 8px

Patch 2 / 3: next in the code flow that shows a menu, we must position
the menu using a getComputedStyle done internally by cu.ui positioning
code. Just before that style recalc, set the menu's margin-top: 8px in
inline style.

The inline style overrides all CSS and all action-bar menu's of files-
app have 8px margin-top as a result (to provide tap-target gap).

Bug: 1066727
Change-Id: Ie6e7a651d8bb974dc71581d460e04debb60892c4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2301713
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Alex Danilo <adanilo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789361}

ui/file_manager/file_manager/foreground/js/ui/multi_menu_button.js

@@ -393,6 +393,11 @@ cr.define('cr.ui', () => {
      */
     positionMenu_() {
       const style = this.menu.style;
+
+      if (util.isFilesNg()) {
+        style.marginTop = '8px';  // crbug.com/1066727
+      }
+
       // Clear any maxHeight we've set from previous calls into here.
       style.maxHeight = 'none';
       const invertLeftRight = false;