Remove CompositedLayerMapping::overflow_controlls_host_layer_

The only purpose of it was to group the overflow control layers.
With it removed, we can make all GraphicsLayers collectable as
GraphicsLayerDisplayItems.

Change-Id: Ic37fa3a3902fa3bb493c2b78b15c1df5bd1f6b4f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2341038Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795942}

third_party/blink/renderer/core/paint/compositing/composited_layer_mapping.cc

@@ -719,7 +719,6 @@ void CompositedLayerMapping::UpdateGraphicsLayerGeometry(
                              snapped_offset_from_composited_ancestor);
 
   UpdateMainGraphicsLayerGeometry(local_compositing_bounds);
-  UpdateOverflowControlsHostLayerGeometry(compositing_container);
   UpdateSquashingLayerGeometry(
       compositing_container, snapped_offset_from_composited_ancestor,
       non_scrolling_squashed_layers_, layers_needing_paint_invalidation);
@@ -790,20 +789,6 @@ void CompositedLayerMapping::ComputeGraphicsLayerParentLocation(
   }
 }
 
-void CompositedLayerMapping::UpdateOverflowControlsHostLayerGeometry(
-    const PaintLayer* compositing_container) {
-  if (!overflow_controls_host_layer_)
-    return;
-
-  // To clip the scrollbars correctly, overflow_controls_host_layer_ should
-  // match our border box size.
-  const IntSize border_box_size =
-      owning_layer_.GetLayoutBox()->PixelSnappedBorderBoxSize(
-          PhysicalOffset(owning_layer_.SubpixelAccumulation() +
-                         owning_layer_.GetLayoutBox()->PhysicalLocation()));
-  overflow_controls_host_layer_->SetSize(gfx::Size(border_box_size));
-}
-
 void CompositedLayerMapping::UpdateMaskLayerGeometry() {
   if (!mask_layer_)
     return;
@@ -945,20 +930,12 @@ void CompositedLayerMapping::UpdateInternalHierarchy() {
   if (scrolling_contents_layer_)
     graphics_layer_->AddChild(scrolling_contents_layer_.get());
 
-  // Now constructing the subtree for the overflow controls.
-  if (overflow_controls_host_layer_) {
-    graphics_layer_->AddChild(overflow_controls_host_layer_.get());
-    if (layer_for_horizontal_scrollbar_) {
-      overflow_controls_host_layer_->AddChild(
-          layer_for_horizontal_scrollbar_.get());
-    }
-    if (layer_for_vertical_scrollbar_) {
-      overflow_controls_host_layer_->AddChild(
-          layer_for_vertical_scrollbar_.get());
-    }
+  if (layer_for_horizontal_scrollbar_)
+    graphics_layer_->AddChild(layer_for_horizontal_scrollbar_.get());
+  if (layer_for_vertical_scrollbar_)
+    graphics_layer_->AddChild(layer_for_vertical_scrollbar_.get());
   if (layer_for_scroll_corner_)
-      overflow_controls_host_layer_->AddChild(layer_for_scroll_corner_.get());
-  }
+    graphics_layer_->AddChild(layer_for_scroll_corner_.get());
 
   if (decoration_outline_layer_)
     graphics_layer_->AddChild(decoration_outline_layer_.get());
@@ -1136,13 +1113,6 @@ bool CompositedLayerMapping::UpdateOverflowControlsLayers(
       layer_for_scroll_corner_, needs_scroll_corner_layer,
       CompositingReason::kLayerForScrollCorner);
 
-  bool needs_overflow_controls_host_layer = needs_horizontal_scrollbar_layer ||
-                                            needs_vertical_scrollbar_layer ||
-                                            needs_scroll_corner_layer;
-  ToggleScrollbarLayerIfNeeded(
-      overflow_controls_host_layer_, needs_overflow_controls_host_layer,
-      CompositingReason::kLayerForOverflowControlsHost);
-
   return horizontal_scrollbar_layer_changed ||
          vertical_scrollbar_layer_changed || scroll_corner_layer_changed;
 }
@@ -1524,10 +1494,21 @@ bool CompositedLayerMapping::NeedsToReparentOverflowControls() const {
   return owning_layer_.NeedsReorderOverlayOverflowControls();
 }
 
-GraphicsLayer* CompositedLayerMapping::DetachLayerForOverflowControls() {
-  if (overflow_controls_host_layer_)
-    overflow_controls_host_layer_->RemoveFromParent();
-  return overflow_controls_host_layer_.get();
+wtf_size_t CompositedLayerMapping::MoveOverflowControlLayersInto(
+    GraphicsLayerVector& vector,
+    wtf_size_t position) {
+  wtf_size_t count = 0;
+  auto move_layer = [&](GraphicsLayer* layer) {
+    if (!layer)
+      return;
+    layer->RemoveFromParent();
+    vector.insert(position++, layer);
+    count++;
+  };
+  move_layer(layer_for_horizontal_scrollbar_.get());
+  move_layer(layer_for_vertical_scrollbar_.get());
+  move_layer(layer_for_scroll_corner_.get());
+  return count;
 }
 
 GraphicsLayer* CompositedLayerMapping::ParentForSublayers() const {
@@ -1552,7 +1533,9 @@ void CompositedLayerMapping::SetSublayers(
         if (layer && layer->Parent() == parent)
           layers_needing_reattachment.push_back(layer);
       };
-  add_layer_needing_reattachment(overflow_controls_host_layer_.get());
+  add_layer_needing_reattachment(layer_for_horizontal_scrollbar_.get());
+  add_layer_needing_reattachment(layer_for_vertical_scrollbar_.get());
+  add_layer_needing_reattachment(layer_for_scroll_corner_.get());
   add_layer_needing_reattachment(decoration_outline_layer_.get());
   add_layer_needing_reattachment(mask_layer_.get());
   add_layer_needing_reattachment(non_scrolling_squashing_layer_.get());
@@ -2326,8 +2309,6 @@ String CompositedLayerMapping::DebugName(
     name = "Vertical Scrollbar Layer";
   } else if (graphics_layer == layer_for_scroll_corner_.get()) {
     name = "Scroll Corner Layer";
-  } else if (graphics_layer == overflow_controls_host_layer_.get()) {
-    name = "Overflow Controls Host Layer";
   } else if (graphics_layer == scrolling_contents_layer_.get()) {
     name = "Scrolling Contents Layer";
   } else if (graphics_layer == decoration_outline_layer_.get()) {

third_party/blink/renderer/core/paint/compositing/composited_layer_mapping.h

@@ -210,10 +210,10 @@ class CORE_EXPORT CompositedLayerMapping final : public GraphicsLayerClient {
   // scrolling content.
   bool NeedsToReparentOverflowControls() const;
 
-  // Removes the overflow controls host layer from its parent and positions it
-  // so that it can be inserted as a sibling to this CLM without changing
-  // position.
-  GraphicsLayer* DetachLayerForOverflowControls();
+  // Move overflow control layers from its parent into the vector.
+  // Returns the number of layers moved.
+  wtf_size_t MoveOverflowControlLayersInto(GraphicsLayerVector&,
+                                           wtf_size_t position);
 
   void SetBlendMode(BlendMode);
 
@@ -312,9 +312,6 @@ class CORE_EXPORT CompositedLayerMapping final : public GraphicsLayerClient {
       Vector<GraphicsLayerPaintInfo>& layers,
       Vector<PaintLayer*>& layers_needing_paint_invalidation);
   void UpdateMainGraphicsLayerGeometry(const IntRect& local_compositing_bounds);
-  void UpdateOverflowControlsHostLayerGeometry(
-      const PaintLayer* compositing_container);
-  void UpdateChildTransformLayerGeometry();
   void UpdateMaskLayerGeometry();
   void UpdateForegroundLayerGeometry();
   void UpdateDecorationOutlineLayerGeometry(
@@ -412,10 +409,9 @@ class CORE_EXPORT CompositedLayerMapping final : public GraphicsLayerClient {
   //
   //    + graphics_layer_
   //      + contents layers (or contents layers under scrolling_contents_layer_)
-  //      + overflow_controls_host_layer_ [OPTIONAL]
-  //      | + layer_for_vertical_scrollbar_ [OPTIONAL]
-  //      | + layer_for_horizontal_scrollbar_ [OPTIONAL]
-  //      | + layer_for_scroll_corner_ [OPTIONAL]
+  //      + layer_for_vertical_scrollbar_ [OPTIONAL]
+  //      + layer_for_horizontal_scrollbar_ [OPTIONAL]
+  //      + layer_for_scroll_corner_ [OPTIONAL]
   //      + decoration_outline_layer_ [OPTIONAL]
   //      + mask_layer_ [ OPTIONAL ]
   //      + non_scrolling_squashing_layer_ [ OPTIONAL ]
@@ -457,12 +453,6 @@ class CORE_EXPORT CompositedLayerMapping final : public GraphicsLayerClient {
   std::unique_ptr<GraphicsLayer> layer_for_vertical_scrollbar_;
   std::unique_ptr<GraphicsLayer> layer_for_scroll_corner_;
 
-  // This layer contains the scrollbar and scroll corner layers and clips them
-  // to the border box bounds of our LayoutObject. It is usually added to
-  // graphics_layer_, but may be reparented by GraphicsLayerTreeBuilder to
-  // ensure that scrollbars appear above scrolling content.
-  std::unique_ptr<GraphicsLayer> overflow_controls_host_layer_;
-
   // DecorationLayer which paints outline.
   std::unique_ptr<GraphicsLayer> decoration_outline_layer_;
 

third_party/blink/renderer/core/paint/compositing/composited_layer_mapping_test.cc

@@ -1709,13 +1709,15 @@ TEST_F(CompositedLayerMappingTest, ContentsOpaque) {
   EXPECT_TRUE(mapping->MainGraphicsLayer()->ContentsOpaque());
 }
 
-TEST_F(CompositedLayerMappingTest, NullOverflowControlsHostLayer) {
+TEST_F(CompositedLayerMappingTest, NullOverflowControlLayers) {
   SetHtmlInnerHTML("<div id='target' style='will-change: transform'></div>");
   CompositedLayerMapping* mapping =
       ToLayoutBoxModelObject(GetLayoutObjectByElementId("target"))
           ->Layer()
           ->GetCompositedLayerMapping();
-  EXPECT_FALSE(mapping->DetachLayerForOverflowControls());
+  EXPECT_FALSE(mapping->LayerForHorizontalScrollbar());
+  EXPECT_FALSE(mapping->LayerForVerticalScrollbar());
+  EXPECT_FALSE(mapping->LayerForScrollCorner());
 }
 
 TEST_F(CompositedLayerMappingTest, CompositedHiddenAnimatingLayer) {

third_party/blink/renderer/core/paint/compositing/graphics_layer_tree_builder.cc

@@ -166,11 +166,9 @@ void GraphicsLayerTreeBuilder::RebuildRecursive(
                 return a.second < b.second;
               });
     for (auto& item : pending) {
-      if (auto* layer = item.first->GetCompositedLayerMapping()
-                            ->DetachLayerForOverflowControls()) {
-        this_layer_children.insert(item.second + offset, layer);
-        offset++;
-      }
+      offset += item.first->GetCompositedLayerMapping()
+                    ->MoveOverflowControlLayersInto(this_layer_children,
+                                                    item.second + offset);
     }
 
     if (!this_layer_children.IsEmpty())

third_party/blink/renderer/platform/graphics/compositing_reasons.cc

@@ -113,9 +113,6 @@ constexpr CompositingReasonStringMap kCompositingReasonsStringMap[] = {
      "Secondary layer, the horizontal scrollbar layer"},
     {CompositingReason::kLayerForVerticalScrollbar, "layerForVerticalScrollbar",
      "Secondary layer, the vertical scrollbar layer"},
-    {CompositingReason::kLayerForOverflowControlsHost,
-     "layerForOverflowControlsHost",
-     "Secondary layer, the overflow controls host layer"},
     {CompositingReason::kLayerForScrollCorner, "layerForScrollCorner",
      "Secondary layer, the scroll corner layer"},
     {CompositingReason::kLayerForScrollingContents, "layerForScrollingContents",

third_party/blink/renderer/platform/graphics/compositing_reasons.h

@@ -74,7 +74,6 @@ using CompositingReasons = uint64_t;
   used in CompositeAfterPaint. */                                             \
   V(LayerForHorizontalScrollbar)                                              \
   V(LayerForVerticalScrollbar)                                                \
-  V(LayerForOverflowControlsHost)                                             \
   V(LayerForScrollCorner)                                                     \
   V(LayerForScrollingContents)                                                \
   V(LayerForSquashingContents)                                                \