Fix issue with descendants of aria-activedescendant being marked as focusable.

third_party/WebKit/Source/modules/accessibility/AXObjectCacheImpl.cpp

Index: third_party/WebKit/Source/modules/accessibility/AXObjectCacheImpl.cpp
diff --git a/third_party/WebKit/Source/modules/accessibility/AXObjectCacheImpl.cpp b/third_party/WebKit/Source/modules/accessibility/AXObjectCacheImpl.cpp
index 7df53a74a50a9c87e7d258b1f3cf56d67559efcf..0f97ca9e294a357df74503a3fa1787c44c0daa24 100644
--- a/third_party/WebKit/Source/modules/accessibility/AXObjectCacheImpl.cpp
+++ b/third_party/WebKit/Source/modules/accessibility/AXObjectCacheImpl.cpp
@@ -983,6 +983,11 @@ void AXObjectCacheImpl::handleAriaSelectedChanged(Node* node)
 
 void AXObjectCacheImpl::handleActiveDescendantChanged(Node* node)
 {
+    // Changing the active descendant should trigger recomputing all
+    // cached values even if it doesn't result in a notification, because
+    // it can affect what's focusable or not.
+    m_modificationCount++;
+
     if (AXObject* obj = getOrCreate(node))
         obj->handleActiveDescendantChanged();
 }