[quickview] Use toggleAttribute for toolbar metadata info-button

Using setAttribute and removeAttribute is an anti-pattern in areas our
code: toggleAttribute can be used to achieve the exact same result.

Add a TODO about this.$.innerContentPanel.focus() not working. Comment
is most likely out-of-date, we'll see.

Bug: 992824
Change-Id: I58ab7ae8418273cde9eb41c78b9a9babfdd9658b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2120775Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Alex Danilo <adanilo@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753505}

ui/file_manager/file_manager/foreground/elements/files_quick_view.js

@@ -182,6 +182,9 @@ const FilesQuickView = Polymer({
   },
 
   /**
+   * TODO(992824): investigate the this.$.innerContentPanel.focus() since the
+   * has no tabindex it seems, and so the focus() call is ignored.
+   *
    * @param {!Event} event tap event.
    *
    * @private
@@ -193,11 +196,7 @@ const FilesQuickView = Polymer({
 
     if (this.hasAttribute('files-ng')) {
       this.metadataBoxActive = !this.metadataBoxActive;
-      if (this.metadataBoxActive) {
-        event.target.setAttribute('toogle', '');
-      } else {
-        event.target.removeAttribute('toogle');
-      }
+      event.target.toggleAttribute('toogle', this.metadataBoxActive);
     }
   },