[directory-tree] Remove TREE_ITEM_INNER_HTML constant

All directory items now derive from TreeItem: this constant is unused,
and can be removed.

Also use this.rowElement for the labelElement in class TreeItem, so it
works in the FILE_NG_ENABLED case as well.

Bug: 992819
Change-Id: I1997e7884adf3a956294acdcf043dec487160e8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1868355
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Reviewed-by: Alex Danilo <adanilo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707323}

ui/file_manager/file_manager/foreground/js/ui/directory_tree.js

@@ -126,14 +126,6 @@ DirectoryItemTreeBaseMethods.recordUMASelectedEntry =
 
 Object.freeze(DirectoryItemTreeBaseMethods);
 
-const TREE_ITEM_INNER_HTML = '<div class="tree-row">' +
-    ' <paper-ripple fit class="recenteringTouch"></paper-ripple>' +
-    ' <span class="expand-icon"></span>' +
-    ' <span class="icon"></span>' +
-    ' <span class="label entry-name"></span>' +
-    '</div>' +
-    '<div class="tree-children" role="group"></div>';
-
 ////////////////////////////////////////////////////////////////////////////////
 // TreeItem
 
@@ -223,7 +215,7 @@ class TreeItem extends cr.ui.TreeItem {
    * @override
    */
   get labelElement() {
-    return this.firstElementChild.querySelector('.label');
+    return this.rowElement.querySelector('.label');
   }
 }
 
@@ -274,7 +266,6 @@ class DirectoryItem extends TreeItem {
     this.onMetadataUpdateBound_ = undefined;
   }
 
-
   /**
    * The DirectoryEntry corresponding to this DirectoryItem. This may be
    * a dummy DirectoryEntry.