[menus] Disable ripple for files-ng menus

Hides the <paper-ripple> elements for files-ng.

Adds a flat color for menu items that are being activated
(e.g. pressed) to provide user feedback when activating a menu item.

Bug: 992825, 1002396
Change-Id: I628cf5668ad03e2f959df9ed5d5e821cd6e0624b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2128000Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#754820}

ui/file_manager/file_manager/foreground/css/menu.css

@@ -99,3 +99,15 @@ cr-menu.files-menu > cr-menu-item > span {
 cr-menu.files-menu > cr-menu-item > paper-ripple {
   z-index: 0;
 }
+
+html.files-ng cr-menu-item > paper-ripple {
+  display: none;
+}
+
+html.files-ng cr-menu.files-menu > cr-menu-item:not([disabled])[selected] {
+  background-color: rgba(0, 0, 0, 4%);
+}
+
+html.files-ng cr-menu.files-menu > cr-menu-item:not([disabled]):active[selected] {
+  background-color: rgba(0, 0, 0, 12%);
+}
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