Bug 1639048 - Don't traverse into labels. r=Jamie

Labels are often used as primary click targets for related inputs. If
they are styled to certain bounds, but contain overflowing text for a11y
with a color of "transparent", the synthesized click will happen outside
the bounds of the label.

If we skip text leafs with "color: transparent", we will skip labels
altogether. Instead, lets land on labels when traversing, and ignore
its subtree.

Differential Revision: https://phabricator.services.mozilla.com/D77898

accessible/android/TraversalRule.cpp

@@ -250,6 +250,13 @@ uint16_t TraversalRule::DefaultMatch(Accessible* aAccessible) {
                nsIAccessibleTraversalRule::FILTER_IGNORE_SUBTREE;
       }
       break;
+    case roles::LABEL:
+      if (IsFlatSubtree(aAccessible)) {
+        // Match if this is a label with text but no nested controls.
+        return nsIAccessibleTraversalRule::FILTER_MATCH |
+               nsIAccessibleTraversalRule::FILTER_IGNORE_SUBTREE;
+      }
+      break;
     case roles::MENUITEM:
     case roles::LINK:
     case roles::PAGETAB:

dom/locales/en-US/chrome/accessibility/AccessFu.properties

@@ -48,7 +48,6 @@ whitespace     =       white space
 pagetablist    =       tab list
 canvas         =       canvas
 checkmenuitem  =       check menu item
-label          =       label
 passwordtext   =       password text
 radiomenuitem  =       radio menu item
 textcontainer  =       text container
@@ -275,7 +274,6 @@ whitespaceAbbr     =       white space
 pagetablistAbbr    =       tab list
 canvasAbbr         =       canvas
 checkmenuitemAbbr  =       check menu item
-labelAbbr          =       label
 passwordtextAbbr   =       passwdtxt
 radiomenuitemAbbr  =       radio menu item
 textcontainerAbbr  =       text container