Clear scroll anchor on all parent scrollers from ScrollAnchor::clear

third_party/WebKit/Source/core/layout/LayoutObject.cpp

Index: third_party/WebKit/Source/core/layout/LayoutObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.cpp b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
index eca6b082996a9c4e144924398fe522653d4adbd0..327710e04f05a609be40ae5442f99349c23f2105 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
@@ -42,6 +42,7 @@
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/html/HTMLElement.h"
+#include "core/html/HTMLFrameOwnerElement.h"
 #include "core/html/HTMLHtmlElement.h"
 #include "core/html/HTMLTableCellElement.h"
 #include "core/html/HTMLTableElement.h"
@@ -2575,39 +2576,65 @@ void LayoutObject::insertedIntoTree() {
     flowThread->flowThreadDescendantWasInserted(this);
 }
 
-enum FindReferencingScrollAnchorsBehavior { DontClear, Clear };
-
-static bool findReferencingScrollAnchors(
-    LayoutObject* layoutObject,
-    FindReferencingScrollAnchorsBehavior behavior) {
+enum FindScrollAnchorsBehavior { FindReferencing, ClearReferencing, ClearAll };
+
+// Returns true if scroller has layoutObject as its anchor.
+static bool clearScrollAnchorForScroller(ScrollableArea* scroller,
+                                         LayoutObject* layoutObject,
+                                         FindScrollAnchorsBehavior behavior) {
+  DCHECK(scroller);
+  ScrollAnchor* anchor = scroller->scrollAnchor();
+  DCHECK(anchor);
+  bool refersTo = false;
+  if (anchor->refersTo(layoutObject)) {
+    refersTo = true;
+    if (behavior == FindReferencing)
+      return refersTo;
+    layoutObject->setIsScrollAnchorObject(false);
+    anchor->releaseAnchor();
+  } else if (behavior == ClearAll && anchor->anchorObject()) {
+    anchor->anchorObject()->setIsScrollAnchorObject(false);
+    anchor->releaseAnchor();
+  }
+  return refersTo;
+}
+
+// Returns true if any of scroller in the parent chain of layoutObject has
+// layoutObject as its anchor. If FindScrollAnchorsBehavior is ClearAll, all
+// the scrollers in the parent chain of layoutObject will have their scroll
+// anchor cleared. If FindScrollAnchorsBehavior is ClearReferencing, all the
+// scrollers in the parent chain of layoutObject that have layoutObject as their
+// anchor will have their scroll anchor cleared.
+static bool findScrollAnchors(LayoutObject* layoutObject,
+                              FindScrollAnchorsBehavior behavior) {
   PaintLayer* layer = nullptr;
   if (LayoutObject* parent = layoutObject->parent())
     layer = parent->enclosingLayer();
   bool found = false;
 
-  // Walk up the layer tree to clear any scroll anchors that reference us.
+  // Walk up the layer tree to clear scroll anchors if required.
   while (layer) {
-    if (PaintLayerScrollableArea* scrollableArea = layer->getScrollableArea()) {
-      ScrollAnchor* anchor = scrollableArea->scrollAnchor();
-      DCHECK(anchor);
-      if (anchor->refersTo(layoutObject)) {
-        found = true;
-        if (behavior == Clear)
-          anchor->notifyRemoved(layoutObject);
-        else
-          return true;
-      }
+    if (PaintLayerScrollableArea* scroller = layer->getScrollableArea()) {
+      found = clearScrollAnchorForScroller(scroller, layoutObject, behavior) ||
+              found;
+      if (found && behavior == FindReferencing)
+        return found;
     }
     layer = layer->parent();
   }
+
   if (FrameView* view = layoutObject->frameView()) {
-    ScrollAnchor* anchor = view->scrollAnchor();
-    DCHECK(anchor);
-    if (anchor->refersTo(layoutObject)) {
-      found = true;
-      if (behavior == Clear)
-        anchor->notifyRemoved(layoutObject);
-    }
+    found = clearScrollAnchorForScroller(view, layoutObject, behavior) || found;
+    if (found && behavior == FindReferencing)
+      return found;
+  }
+
+  // Continue walk past frame boundary.

[skobes, 2016/10/10 21:34:35]

Hmm, do we actually want this behavior?  We don't descend into iframes in
findAnchor, so I don't think iframe scrolls need to clear anchors in parent
frames.

[ymalik, 2016/10/11 19:54:22]

hmm you're right. I was under the impression that we do actually descend into
iframes. But we don't so you're right that we don't need this.

+  if (layoutObject->document().localOwner()) {
+    found =
+        findScrollAnchors(layoutObject->document().localOwner()->layoutObject(),
+                          behavior) ||
+        found;
   }
   return found;
 }
@@ -2641,17 +2668,19 @@ void LayoutObject::willBeRemovedFromTree() {
     parent()->setNeedsBoundariesUpdate();
 
   if (RuntimeEnabledFeatures::scrollAnchoringEnabled() &&
-      m_bitfields.isScrollAnchorObject()) {
-    // Clear the bit first so that anchor.clear() doesn't recurse into findReferencingScrollAnchors.
-    m_bitfields.setIsScrollAnchorObject(false);
-    findReferencingScrollAnchors(this, Clear);
-  }
+      m_bitfields.isScrollAnchorObject())
+    findScrollAnchors(this, ClearReferencing);
 }
 
 void LayoutObject::maybeClearIsScrollAnchorObject() {
-  if (m_bitfields.isScrollAnchorObject())
+  if (m_bitfields.isScrollAnchorObject()) {
     m_bitfields.setIsScrollAnchorObject(
-        findReferencingScrollAnchors(this, DontClear));
+        findScrollAnchors(this, FindReferencing));
+  }
+}
+
+void LayoutObject::clearScrollAnchors() {
+  findScrollAnchors(this, ClearAll);
 }
 
 void LayoutObject::removeFromLayoutFlowThread() {