Refresh z-list when existence of scrollable area of a PaintLayer changes

This is to refresh data for reordering overlay overflow controls.

Bug: 1149793
Change-Id: I94fc45373ba3e5aad684283c6fda6ae5e31581f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2547435Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829077}

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

@@ -1597,22 +1597,24 @@ bool PaintLayer::RequiresScrollableArea() const {
 }
 
 void PaintLayer::UpdateScrollableArea() {
-  if (RequiresScrollableArea() && !scrollable_area_) {
+  if (RequiresScrollableArea() == !!scrollable_area_)
+    return;
+
+  if (!scrollable_area_) {
     scrollable_area_ = MakeGarbageCollected<PaintLayerScrollableArea>(*this);
-    if (Compositor()) {
-      Compositor()->SetNeedsCompositingUpdate(kCompositingUpdateRebuildTree);
-    }
-    GetLayoutObject().SetNeedsPaintPropertyUpdate();
-  } else if (!RequiresScrollableArea() && scrollable_area_) {
+  } else {
     scrollable_area_->Dispose();
     scrollable_area_.Clear();
-    if (Compositor()) {
-      Compositor()->SetNeedsCompositingUpdate(kCompositingUpdateRebuildTree);
-    }
     GetLayoutObject().SetBackgroundPaintLocation(
         kBackgroundPaintInGraphicsLayer);
-    GetLayoutObject().SetNeedsPaintPropertyUpdate();
   }
+
+  GetLayoutObject().SetNeedsPaintPropertyUpdate();
+  // Need to update z-ordering of overlay overflow controls.
+  if (!scrollable_area_ || NeedsReorderOverlayOverflowControls())
+    DirtyStackingContextZOrderLists();
+  if (auto* compositor = Compositor())
+    compositor->SetNeedsCompositingUpdate(kCompositingUpdateRebuildTree);
 }
 
 bool PaintLayer::HasOverflowControls() const {

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

@@ -61,7 +61,7 @@ namespace blink {
 // in order to determine if we isStacked() we have to ask the paint
 // layer about some of its state.
 PaintLayerStackingNode::PaintLayerStackingNode(PaintLayer& layer)
-    : layer_(layer), z_order_lists_dirty_(true) {
+    : layer_(layer) {
   DCHECK(layer.GetLayoutObject().IsStackingContext());
 }
 

third_party/blink/renderer/core/paint/paint_layer_stacking_node.h

@@ -201,7 +201,7 @@ class CORE_EXPORT PaintLayerStackingNode {
   PaintLayers overlay_overflow_controls_reordered_list_;
 
   // Indicates whether the z-order lists above are dirty.
-  bool z_order_lists_dirty_ : 1;
+  bool z_order_lists_dirty_ = true;
 };
 
 }  // namespace blink

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

@@ -465,11 +465,17 @@ class ReorderOverlayOverflowControlsTest
   void InitOverflowStyle(const char* id) {
     GetDocument().getElementById(id)->setAttribute(
         html_names::kStyleAttr, GetOverlayType() == kOverlayScrollbars
-                                    ? "overflow : auto"
+                                    ? "overflow: auto"
                                     : "overflow: hidden; resize: both");
     UpdateAllLifecyclePhasesForTest();
   }
 
+  void RemoveOverflowStyle(const char* id) {
+    GetDocument().getElementById(id)->setAttribute(html_names::kStyleAttr,
+                                                   "overflow: visible");
+    UpdateAllLifecyclePhasesForTest();
+  }
+
   void SetUp() override {
     EnableCompositing();
     RenderingTest::SetUp();
@@ -542,14 +548,14 @@ TEST_P(ReorderOverlayOverflowControlsTest, StackedWithInFlowDescendant) {
 TEST_P(ReorderOverlayOverflowControlsTest, StackedWithOutOfFlowDescendant) {
   SetBodyInnerHTML(R"HTML(
     <style>
-      #child {
-        width: 200px;
-        height: 200px;
-      }
       #parent {
         position: relative;
         height: 100px;
       }
+      #child {
+        width: 200px;
+        height: 200px;
+      }
     </style>
     <div id='parent'>
       <div id='child' style='position: absolute'></div>
@@ -1008,6 +1014,42 @@ TEST_P(ReorderOverlayOverflowControlsTest,
   EXPECT_TRUE(LayersPaintingOverlayOverflowControlsAfter(child));
 }
 
+TEST_P(ReorderOverlayOverflowControlsTest, AddRemoveScrollableArea) {
+  SetBodyInnerHTML(R"HTML(
+    <style>
+      #parent {
+        position: relative;
+        height: 100px;
+      }
+      #child {
+        position: absolute;
+        width: 200px;
+        height: 200px;
+      }
+    </style>
+    <div id='parent'>
+      <div id='child'></div>
+    </div>
+  )HTML");
+
+  auto* parent = GetPaintLayerByElementId("parent");
+  auto* child = GetPaintLayerByElementId("child");
+  EXPECT_FALSE(parent->GetScrollableArea());
+  EXPECT_FALSE(parent->NeedsReorderOverlayOverflowControls());
+  EXPECT_FALSE(LayersPaintingOverlayOverflowControlsAfter(child));
+
+  InitOverflowStyle("parent");
+  EXPECT_TRUE(parent->GetScrollableArea());
+  EXPECT_TRUE(parent->NeedsReorderOverlayOverflowControls());
+  EXPECT_THAT(LayersPaintingOverlayOverflowControlsAfter(child),
+              Pointee(ElementsAre(parent)));
+
+  RemoveOverflowStyle("parent");
+  EXPECT_FALSE(parent->GetScrollableArea());
+  EXPECT_FALSE(parent->NeedsReorderOverlayOverflowControls());
+  EXPECT_FALSE(LayersPaintingOverlayOverflowControlsAfter(child));
+}
+
 TEST_P(PaintLayerTest, SubsequenceCachingStackedLayers) {
   SetBodyInnerHTML(R"HTML(
     <div id='parent' style='position:relative'>