Bug 1703169: Support XUL buttons labelled by text children. r=morgan

Previously, text children were excluded from the a11y tree, so they weren't considered when computing name from subtree.

Differential Revision: https://phabricator.services.mozilla.com/D111029

accessible/tests/mochitest/name/test_general.xhtml

@@ -131,6 +131,9 @@
       // children.
       testName("box_children", "14");
 
+      // Button labelled by a text child.
+      testName("button_text", "Text");
+
       // ARIA role option is presented allowing the name calculation from
       // the visible children (bug 443081)
       testName("lb_opt1_children_hidden", "i am visible");
@@ -299,6 +302,7 @@
 
   <!-- name from children -->
   <box id="box_children" role="button">14</box>
+  <button id="button_text">Text</button>
 
   <!-- name from children, hidden children -->
   <vbox role="listbox" tabindex="0">

accessible/xul/XULFormControlAccessible.cpp

@@ -125,10 +125,16 @@ LocalAccessible* XULButtonAccessible::ContainerWidget() const {
 }
 
 bool XULButtonAccessible::IsAcceptableChild(nsIContent* aEl) const {
-  // In general XUL button has not accessible children. Nevertheless menu
-  // buttons can have popup accessibles (@type="menu" or columnpicker).
-  return aEl->IsXULElement(nsGkAtoms::menupopup) ||
-         aEl->IsXULElement(nsGkAtoms::popup);
+  // In general XUL buttons should not have accessible children. However:
+  return
+      //   menu buttons can have popup accessibles (@type="menu" or
+      //   columnpicker).
+      aEl->IsXULElement(nsGkAtoms::menupopup) ||
+      aEl->IsXULElement(nsGkAtoms::popup) ||
+      // A XUL button can be labelled by a child text node, so we need to allow
+      // that as a child so it will be picked up when computing name from
+      // subtree.
+      aEl->IsText();
 }
 
 ////////////////////////////////////////////////////////////////////////////////