Bug 1780878: [Part 3] Cache FLOWS_TO and FLOWS_FROM relations r=Jamie

Differential Revision: https://phabricator.services.mozilla.com/D152581

accessible/base/CacheConstants.h

@@ -75,6 +75,8 @@ static constexpr RelationData kRelationTypeAtoms[] = {
      RelationType::CONTROLLER_FOR},
     {nsGkAtoms::aria_describedby, nullptr, RelationType::DESCRIBED_BY,
      RelationType::DESCRIPTION_FOR},
+    {nsGkAtoms::aria_flowto, nullptr, RelationType::FLOWS_TO,
+     RelationType::FLOWS_FROM},
 };
 
 }  // namespace a11y

accessible/generic/LocalAccessible.cpp

@@ -1375,7 +1375,8 @@ void LocalAccessible::DOMAttributeChanged(int32_t aNameSpaceID,
     SendCache(CacheDomain::Actions, CacheUpdateType::Update);
   }
 
-  if (aAttribute == nsGkAtoms::aria_controls) {
+  if (aAttribute == nsGkAtoms::aria_controls ||
+      aAttribute == nsGkAtoms::aria_flowto) {
     mDoc->QueueCacheUpdate(this, CacheDomain::Relations);
   }