[DL]: Add NearestLockedInclusiveAncestor to DisplayLockUtilities

This CL adds a new function, NearestLockedInclusiveAncestor, to
DisplayLockUtilties, so that it can be reused in multiple places
(example: https://chromium-review.googlesource.com/c/chromium/src/+/1528123/2/third_party/blink/renderer/core/inspector/inspector_highlight.cc#291)

Bug: 882663
Change-Id: Ia7408f10635f7304cebee483c14773c626d6bec3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1528126Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: vmpstr <vmpstr@chromium.org>
Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642361}

third_party/blink/renderer/core/css/style_engine.cc

@@ -48,6 +48,7 @@
 #include "third_party/blink/renderer/core/css/style_change_reason.h"
 #include "third_party/blink/renderer/core/css/style_environment_variables.h"
 #include "third_party/blink/renderer/core/css/style_sheet_contents.h"
+#include "third_party/blink/renderer/core/display_lock/display_lock_utilities.h"
 #include "third_party/blink/renderer/core/dom/element.h"
 #include "third_party/blink/renderer/core/dom/element_traversal.h"
 #include "third_party/blink/renderer/core/dom/flat_tree_traversal.h"
@@ -1575,30 +1576,16 @@ void StyleEngine::MarkForWhitespaceReattachment() {
   for (auto element : whitespace_reattach_set_) {
     if (element->NeedsReattachLayoutTree() || !element->GetLayoutObject())
       continue;
-    if (RuntimeEnabledFeatures::DisplayLockingEnabled() &&
-        GetDocument().LockedDisplayLockCount() > 0) {
       // This element might be located inside a display locked subtree, so we
       // might mark it for ReattachLayoutTree later on instead.
-      // TODO(crbug.com/924550): Once we figure out a more efficient way to
-      // determine whether we're inside a locked subtree or not, change this.
-      bool is_in_locked_subtree = false;
-      for (const Node& ancestor :
-           FlatTreeTraversal::InclusiveAncestorsOf(*element)) {
-        if (!ancestor.IsElementNode())
-          continue;
-        if (auto* context = ToElement(ancestor).GetDisplayLockContext()) {
-          if (!context->IsLocked())
-            continue;
-          is_in_locked_subtree = true;
-          context->AddToWhitespaceReattachSet(*element);
-          break;
-        }
-      }
-      if (is_in_locked_subtree)
-        continue;
+    if (Element* locked_ancestor =
+            DisplayLockUtilities::NearestLockedInclusiveAncestor(*element)) {
+      locked_ancestor->GetDisplayLockContext()->AddToWhitespaceReattachSet(
+          *element);
+      continue;
+    }
       DCHECK(!element->NeedsStyleRecalc());
       DCHECK(!element->ChildNeedsStyleRecalc());
-    }
     if (Node* first_child = LayoutTreeBuilderTraversal::FirstChild(*element))
       first_child->MarkAncestorsWithChildNeedsReattachLayoutTree();
   }

third_party/blink/renderer/core/display_lock/display_lock_utilities.cc

@@ -80,4 +80,23 @@ DisplayLockUtilities::ScopedChainForcedUpdate::ScopedChainForcedUpdate(
   }
 }
 
+Element* DisplayLockUtilities::NearestLockedInclusiveAncestor(
+    const Node& node) {
+  if (!RuntimeEnabledFeatures::DisplayLockingEnabled() ||
+      node.GetDocument().LockedDisplayLockCount() == 0) {
+    return nullptr;
+  }
+  // TODO(crbug.com/924550): Once we figure out a more efficient way to
+  // determine whether we're inside a locked subtree or not, change this.
+  for (Node& ancestor : FlatTreeTraversal::InclusiveAncestorsOf(node)) {
+    if (!ancestor.IsElementNode())
+      continue;
+    if (auto* context = ToElement(ancestor).GetDisplayLockContext()) {
+      if (context->IsLocked())
+        return &ToElement(ancestor);
+    }
+  }
+  return nullptr;
+}
+
 }  // namespace blink

third_party/blink/renderer/core/display_lock/display_lock_utilities.h

@@ -42,6 +42,9 @@ class CORE_EXPORT DisplayLockUtilities {
   // activatable-locked).
   static const HeapVector<Member<Element>> ActivatableLockedInclusiveAncestors(
       Element& element);
+
+  // Returns the nearest inclusive ancestor of |node| that is display locked.
+  static Element* NearestLockedInclusiveAncestor(const Node& node);
 };
 
 }  // namespace blink