Make files-ng focus ring hidden on activation

Bug: 992823
Change-Id: I7002df4a6c8d65e0b57ebe8dad9c6e475dbd2adb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2053676
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741000}

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

@@ -484,7 +484,7 @@ body[type='open-multi-file'].check-select .dialog-header {
   width: 48px;
 }
 
-.dialog-header.files-ng cr-button:focus {
+.dialog-header.files-ng cr-button:focus:not(:active) {
   border: 1px solid var(--google-blue-600);
 }