Use DCHECKs to prevent recursive calls in AXObjectCacheImpl

Add DCHECKs to prevent recursion for ProcessDeferredAccessibilityEvents() and UpdateAXForAllDocuments().
By adding the DCHECK to ProcessDeferredAccessibilityEvents(), we
prove that we can remove an early return that was added.

Bug: None
Change-Id: I53c3e500c0a98ea6e273cf887c511d9bc150c797
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3970627
Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Auto-Submit: Aaron Leventhal <aleventhal@chromium.org>
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1063131}

third_party/blink/renderer/modules/accessibility/ax_object_cache_impl.cc

@@ -719,9 +719,13 @@ void AXObjectCacheImpl::UpdateLifecycleIfNeeded(Document& document) {
 }
 
 void AXObjectCacheImpl::UpdateAXForAllDocuments() {
+#if DCHECK_IS_ON()
   DCHECK(!IsFrozen())
       << "Don't call UpdateAXForAllDocuments() here; layout and a11y are "
          "already clean at the start of serialization.";
+  DCHECK(!updating_layout_and_ax_) << "Undesirable recursion.";
+  base::AutoReset<bool> updating(&updating_layout_and_ax_, true);
+#endif
 
   // First update the layout for the main and popup document.
   UpdateLifecycleIfNeeded(GetDocument());
@@ -2466,11 +2470,7 @@ void AXObjectCacheImpl::ProcessDeferredAccessibilityEvents(Document& document) {
 
   DCHECK_EQ(document, GetDocument());
 
-  if (processing_deferred_events_) {
-    // TODO(aleventhal) Perhaps the caller should be responsible for this:
-    // consider changing to a DCHECK.
-    return;
-  }
+  DCHECK(!processing_deferred_events_);
 
   if (IsDirty()) {
     if (GetPopupDocumentIfShowing()) {
@@ -2915,7 +2915,6 @@ void AXObjectCacheImpl::FireAXEventImmediately(
     ax::mojom::blink::Action event_from_action,
     const BlinkAXEventIntentsSet& event_intents) {
 #if DCHECK_IS_ON()
-  DCHECK(processing_deferred_events_);
   // Make sure none of the layout views are in the process of being laid out.
   // Notifications should only be sent after the layoutObject has finished
   auto* ax_layout_object = DynamicTo<AXLayoutObject>(obj);

third_party/blink/renderer/modules/accessibility/ax_object_cache_impl.h

@@ -670,6 +670,9 @@ class MODULES_EXPORT AXObjectCacheImpl
   std::unique_ptr<AXRelationCache> relation_cache_;
 
   bool processing_deferred_events_ = false;
+#if DCHECK_IS_ON()
+  bool updating_layout_and_ax_ = false;
+#endif
 
   // Verified when finalizing.
   bool has_been_disposed_ = false;