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 87e07f5bf1700c7a5f5cc85c95d46bc1edcbe15b..937fb114b98b2ee56154021be5dc9c5abc7356bc 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"
@@ -2577,39 +2578,65 @@ 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,

[ymalik, 2016/10/06 19:51:13]

@skobes, a note to make reviewing easier.

This function can be called in 3 different ways.
FindReferencing: This will walk up the parent chain and return true of
layoutObject is referenced by any other scroller. This is used when we want to
set the isScrollAnchorObject when a scroll anchor is cleared for only a single
scroller (for cases like these:
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/layout/Sc...)

ClearReferencing: This will walk up the parent chain and clear the anchors for
scrollers that reference layoutObject. This is needed when an element is removed
from the tree. In this case, we don't want to clear anchors for all scroller in
the parent chain.

ClearAll: This will clear scroll anchors for all parent scrollers of
layoutObject. This is when a non-anchoring scroll happens on a child 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.
+  if (layoutObject->document().localOwner()) {
+    found =
+        findScrollAnchors(layoutObject->document().localOwner()->layoutObject(),
+                          behavior) ||
+        found;
   }
   return found;
 }
@@ -2643,17 +2670,19 @@ 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() {