Clear scroll anchors on change of the overflow-anchor property.

In such cases, the chosen anchor may change arbitrarily.

Bug: 924256

Change-Id: I3f304450c59bc3e27b93089469d6fbee68a166e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2008617Reviewed-by: Nick Burris <nburris@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734586}

third_party/blink/renderer/core/layout/layout_object.cc

@@ -2382,6 +2382,22 @@ void LayoutObject::SetScrollAnchorDisablingStyleChangedOnAncestor() {
   }
 }
 
+static void ClearAncestorScrollAnchors(LayoutObject* layout_object) {
+  PaintLayer* layer = nullptr;
+  if (LayoutObject* parent = layout_object->Parent())
+    layer = parent->EnclosingLayer();
+
+  while (layer) {
+    if (PaintLayerScrollableArea* scrollable_area =
+            layer->GetScrollableArea()) {
+      ScrollAnchor* anchor = scrollable_area->GetScrollAnchor();
+      DCHECK(anchor);
+      anchor->Clear();
+    }
+    layer = layer->Parent();
+  }
+}
+
 void LayoutObject::StyleDidChange(StyleDifference diff,
                                   const ComputedStyle* old_style) {
   // First assume the outline will be affected. It may be updated when we know
@@ -2449,6 +2465,10 @@ void LayoutObject::StyleDidChange(StyleDifference diff,
     AddSubtreePaintPropertyUpdateReason(
         SubtreePaintPropertyUpdateReason::kTransformStyleChanged);
   }
+
+  if (old_style && old_style->OverflowAnchor() != StyleRef().OverflowAnchor()) {
+    ClearAncestorScrollAnchors(this);
+  }
 }
 
 void LayoutObject::ApplyPseudoElementStyleChanges(

third_party/blink/web_tests/external/wpt/css/css-scroll-anchoring/opt-out-dynamic-expected.txt

-This is a testharness.js-based test.
-FAIL Dynamically styling 'overflow-anchor: none' on the anchor node should prevent scroll anchoring assert_equals: expected 150 but got 200
-Harness: the test ran to completion.
-