[filesapp] Add fake mouse test events to pointer-active handler list

Test helper fakeEvent does not convert mouse events to pointer events,
so add them to the pointer-active handler list for testing purposes.

Bug: 1062902
Change-Id: I1feef4dde4f8814fb64fd6e3a246947b3d277dbf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2114513Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#752361}

ui/file_manager/file_manager/foreground/js/ui/file_manager_ui.js

@@ -433,8 +433,11 @@ class FileManagerUI {
     document.defaultView.addEventListener('resize', this.relayout.bind(this));
 
     // Add global pointer-active handler.
+    const pointerActiveEvents = window.IN_TEST ?
+        ['pointerdown', 'pointerup', 'mousedown', 'mouseup'] :
+        ['pointerdown', 'pointerup'];
     const rootElement = document.documentElement;
-    ['pointerdown', 'pointerup'].forEach((eventType) => {
+    pointerActiveEvents.forEach((eventType) => {
       document.addEventListener(eventType, (e) => {
         rootElement.classList.toggle('pointer-active', /down$/.test(e.type));
       }, true);