Improved accessibility of treeview control used in internal pages.

ui/webui/resources/js/cr/ui/tree.js

Index: ui/webui/resources/js/cr/ui/tree.js
diff --git a/ui/webui/resources/js/cr/ui/tree.js b/ui/webui/resources/js/cr/ui/tree.js
index aa9199e9c2dadd42a6aa61f2164e799bc15842ad..c7bfe49eab67631fd5e9749c6933dcda078723d3 100644
--- a/ui/webui/resources/js/cr/ui/tree.js
+++ b/ui/webui/resources/js/cr/ui/tree.js
@@ -256,7 +256,7 @@ cr.define('cr.ui', function() {
         '<span class=expand-icon></span>' +
         '<span class=tree-label></span>' +
         '</div>' +
-        '<div class=tree-children></div>';
+        '<div class=tree-children role=group></div>';

[dpapad, 2016/08/03 20:31:19]

All those class= statements are missing quotes, should be

class="expand-icon"
class="tree-label"
class="tree-children"
role="group"

     treeItem.setAttribute('role', 'treeitem');
     return treeItem;
   })();
@@ -280,7 +280,10 @@ cr.define('cr.ui', function() {
      * Initializes the element.
      */
     decorate: function() {
-
+      var labelId = 'tree-item-label-autogen-id-' +
+          treeItemAutoGeneratedIdCounter;
+      this.labelElement.id = labelId;
+      this.setAttribute('aria-labelledby', labelId);
     },
 
     /**
@@ -393,6 +396,7 @@ cr.define('cr.ui', function() {
       if (b) {
         if (this.mayHaveChildren_) {
           this.setAttribute('expanded', '');
+          this.setAttribute('aria-expanded', 'true');
           treeChildren.setAttribute('expanded', '');
           cr.dispatchSimpleEvent(this, 'expand', true);
           this.scrollIntoViewIfNeeded(false);
@@ -405,6 +409,11 @@ cr.define('cr.ui', function() {
             this.selected = true;
         }
         this.removeAttribute('expanded');
+        if (this.mayHaveChildren_) {

[dpapad, 2016/08/03 20:31:19]

Nit: No need for curly braces.

+          this.setAttribute('aria-expanded', 'false');
+        } else {
+          this.removeAttribute('aria-expanded');
+        }
         treeChildren.removeAttribute('expanded');
         cr.dispatchSimpleEvent(this, 'collapse', true);
       }
@@ -520,8 +529,10 @@ cr.define('cr.ui', function() {
       var rowItem = this.firstElementChild;
       this.setAttribute('has-children', b);
       rowItem.setAttribute('has-children', b);
-      if (b)
+      if (b) {
         this.mayHaveChildren_ = true;
+        this.setAttribute('aria-expanded', 'false');
+      }
     },
 
     /**