Optimize performance of containing block chain for subtree layout.

A previous patch regressed performance due to the need to walk the
containing block chain to find containing scrollable areas, in order
to notify them of anchor adjustments.

This patch iterates over all ScrollableAreas and notifies each of them.

Bug: 1024434

Change-Id: Ibee4d9383ec1456c5e020c95aea941124fca048b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1931148
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720361}

third_party/blink/renderer/core/frame/local_frame_view.cc

@@ -605,17 +605,14 @@ void LocalFrameView::PerformPreLayoutTasks() {
 
 void LocalFrameView::LayoutFromRootObject(LayoutObject& root) {
   LayoutState layout_state(root);
-  // Since we are starting layout from an arbitrary node, we need to notify all
-  // possible scroll anchors above us, as they aren't notified during layout.
-  for (auto* ancestor = root.Container(); ancestor;
-       ancestor = ancestor->Container()) {
-    if (ancestor->HasOverflowClip() && ancestor->IsLayoutBlock()) {
-      auto* scrollable_area =
-          ToLayoutBoxModelObject(ancestor)->GetScrollableArea();
-      DCHECK(scrollable_area);
-      scrollable_area->GetScrollAnchor()->NotifyBeforeLayout();
+  if (scrollable_areas_) {
+    for (auto& scrollable_area : *scrollable_areas_) {
+      if (scrollable_area->GetScrollAnchor() &&
+          scrollable_area->ShouldPerformScrollAnchoring())
+        scrollable_area->GetScrollAnchor()->NotifyBeforeLayout();
     }
   }
+
   root.UpdateLayout();
 }
 

third_party/blink/renderer/core/input/gesture_manager.cc

@@ -448,7 +448,7 @@ WebInputEventResult GestureManager::HandleGestureShowPress() {
     return WebInputEventResult::kNotHandled;
   for (const PaintLayerScrollableArea* scrollable_area : *areas) {
     ScrollAnimatorBase* animator = scrollable_area->ExistingScrollAnimator();
-    if (animator)
+    if (scrollable_area->ScrollsOverflow() && animator)
       animator->CancelAnimation();
   }
   return WebInputEventResult::kNotHandled;

third_party/blink/renderer/core/page/page.cc

@@ -742,9 +742,11 @@ void Page::SettingsChanged(SettingsDelegate::ChangeType change_type) {
         if (LocalFrameView* view = local_frame->View()) {
           if (const auto* scrollable_areas = view->ScrollableAreas()) {
             for (const auto& scrollable_area : *scrollable_areas) {
-              if (auto* layout_box = scrollable_area->GetLayoutBox()) {
-                layout_box->SetNeedsLayout(
-                    layout_invalidation_reason::kScrollbarChanged);
+              if (scrollable_area->ScrollsOverflow()) {
+                if (auto* layout_box = scrollable_area->GetLayoutBox()) {
+                  layout_box->SetNeedsLayout(
+                      layout_invalidation_reason::kScrollbarChanged);
+                }
               }
             }
           }

third_party/blink/renderer/core/paint/paint_layer_scrollable_area.cc

@@ -147,6 +147,16 @@ PaintLayerScrollableArea::PaintLayerScrollableArea(PaintLayer& layer)
 
   GetLayoutBox()->GetDocument().GetSnapCoordinator().AddSnapContainer(
       *GetLayoutBox());
+
+  LocalFrame* frame = GetLayoutBox()->GetFrame();
+  if (!frame)
+    return;
+
+  LocalFrameView* frame_view = frame->View();
+  if (!frame_view)
+    return;
+
+  frame_view->AddScrollableArea(this);
 }
 
 PaintLayerScrollableArea::~PaintLayerScrollableArea() {
@@ -2199,6 +2209,7 @@ void PaintLayerScrollableArea::UpdateScrollableAreaSet() {
         v_mode == ScrollbarMode::kAlwaysOff)
       has_overflow = false;
   }
+
   scrolls_overflow_ = has_overflow && is_visible_to_hit_test;
   if (did_scroll_overflow == ScrollsOverflow())
     return;
@@ -2237,13 +2248,6 @@ void PaintLayerScrollableArea::UpdateScrollableAreaSet() {
   // (see: BoxPainter::PaintBoxDecorationBackground).
   GetLayoutBox()->SetBackgroundNeedsFullPaintInvalidation();
 
-  if (scrolls_overflow_) {
-    DCHECK(CanHaveOverflowScrollbars(*GetLayoutBox()));
-    frame_view->AddScrollableArea(this);
-  } else {
-    frame_view->RemoveScrollableArea(this);
-  }
-
   layer_->DidUpdateScrollsOverflow();
 }
 

third_party/blink/renderer/core/testing/internals.cc

@@ -2065,15 +2065,24 @@ unsigned Internals::numberOfScrollableAreas(Document* document) {
 
   unsigned count = 0;
   LocalFrame* frame = document->GetFrame();
-  if (frame->View()->ScrollableAreas())
-    count += frame->View()->ScrollableAreas()->size();
+  if (frame->View()->ScrollableAreas()) {
+    for (const auto& scrollable_area : *frame->View()->ScrollableAreas()) {
+      if (scrollable_area->ScrollsOverflow())
+        count++;
+    }
+  }
 
   for (Frame* child = frame->Tree().FirstChild(); child;
        child = child->Tree().NextSibling()) {
     auto* child_local_frame = DynamicTo<LocalFrame>(child);
     if (child_local_frame && child_local_frame->View() &&
-        child_local_frame->View()->ScrollableAreas())
-      count += child_local_frame->View()->ScrollableAreas()->size();
+        child_local_frame->View()->ScrollableAreas()) {
+      for (const auto& scrollable_area :
+           *child_local_frame->View()->ScrollableAreas()) {
+        if (scrollable_area->ScrollsOverflow())
+          count++;
+      }
+    }
   }
 
   return count;