Remove SlotsInFlatTree Runtime flag

BUG=859429

Change-Id: Iaa998db509f9c9b4a38c2af1fa3c6be576e2d27f
Reviewed-on: https://chromium-review.googlesource.com/1160068
Commit-Queue: Kyoko Muto <kymuto@google.com>
Reviewed-by: Hayato Ito <hayato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581833}

third_party/blink/renderer/core/css/css_computed_style_declaration_test.cc

@@ -60,8 +60,7 @@ TEST_F(CSSComputedStyleDeclarationTest, CleanShadowAncestorsNoRecalc) {
 
   EXPECT_STREQ("rgb(0, 128, 0)",
                computed->GetPropertyValue(CSSPropertyColor).Utf8().data());
-  EXPECT_EQ(RuntimeEnabledFeatures::SlotInFlatTreeEnabled(),
-            GetDocument().NeedsLayoutTreeUpdate());
+  EXPECT_TRUE(GetDocument().NeedsLayoutTreeUpdate());
 }
 
 }  // namespace blink

third_party/blink/renderer/core/dom/flat_tree_traversal_test.cc

@@ -27,12 +27,9 @@ namespace blink {
 namespace flat_tree_traversal_test {
 
 class FlatTreeTraversalTest : public PageTestBase,
-                              private ScopedSlotInFlatTreeForTest,
                               ScopedIncrementalShadowDOMForTest {
  public:
-  FlatTreeTraversalTest()
-      : ScopedSlotInFlatTreeForTest(true),
-        ScopedIncrementalShadowDOMForTest(true) {}
+  FlatTreeTraversalTest() : ScopedIncrementalShadowDOMForTest(true) {}
 
  protected:
   // Sets |mainHTML| to BODY element with |innerHTML| property and attaches

third_party/blink/renderer/core/dom/node.cc

@@ -876,10 +876,7 @@ static ContainerNode* GetReattachParent(Node& node) {
   if (node.IsPseudoElement())
     return node.ParentOrShadowHostNode();
   if (node.IsChildOfV1ShadowHost()) {
-    HTMLSlotElement* slot = RuntimeEnabledFeatures::SlotInFlatTreeEnabled()
-                                ? node.AssignedSlot()
-                                : node.FinalDestinationSlot();
-    if (slot)
+    if (HTMLSlotElement* slot = node.AssignedSlot())
       return slot;
   }
   if (node.IsInV0ShadowTree() || node.IsChildOfV0ShadowHost()) {
@@ -1181,10 +1178,7 @@ bool Node::IsStyledElement() const {
 
 bool Node::CanParticipateInFlatTree() const {
   // TODO(hayato): Return false for pseudo elements.
-  if (RuntimeEnabledFeatures::SlotInFlatTreeEnabled()) {
     return !IsShadowRoot() && !IsActiveV0InsertionPoint(*this);
-  }
-  return !IsShadowRoot() && !IsActiveSlotOrActiveV0InsertionPoint();
 }
 
 bool Node::IsActiveSlotOrActiveV0InsertionPoint() const {

third_party/blink/renderer/core/html/html_slot_element.cc

@@ -231,7 +231,6 @@ void HTMLSlotElement::AppendDistributedNodesFrom(const HTMLSlotElement& other) {
   for (const auto& node : other.distributed_nodes_)
     distributed_indices_.Set(node.Get(), index++);
 }
-
 void HTMLSlotElement::ClearAssignedNodes() {
   DCHECK(RuntimeEnabledFeatures::IncrementalShadowDOMEnabled());
   assigned_nodes_.clear();
@@ -357,17 +356,12 @@ void HTMLSlotElement::AttachLayoutTree(AttachContext& context) {
 // of IncementalShadowDOM.
 const HeapVector<Member<Node>>&
 HTMLSlotElement::ChildrenInFlatTreeIfAssignmentIsSupported() {
-  if (RuntimeEnabledFeatures::SlotInFlatTreeEnabled())
   return AssignedNodes();
-  DCHECK(!NeedsDistributionRecalc());
-  return distributed_nodes_;
 }
 
 void HTMLSlotElement::DetachLayoutTree(const AttachContext& context) {
   if (SupportsAssignment()) {
-    const HeapVector<Member<Node>>& flat_tree_children =
-        RuntimeEnabledFeatures::SlotInFlatTreeEnabled() ? assigned_nodes_
-                                                        : distributed_nodes_;
+    const HeapVector<Member<Node>>& flat_tree_children = assigned_nodes_;
     for (auto& node : flat_tree_children)
       node->LazyReattachIfAttached();
   }
@@ -490,24 +484,8 @@ void HTMLSlotElement::RemovedFrom(ContainerNode* insertion_point) {
   HTMLElement::RemovedFrom(insertion_point);
 }
 
-void HTMLSlotElement::WillRecalcStyle(StyleRecalcChange change) {
-  if (RuntimeEnabledFeatures::SlotInFlatTreeEnabled())
-    return;
-  if (change < kIndependentInherit &&
-      GetStyleChangeType() < kSubtreeStyleChange) {
-    return;
-  }
-  for (auto& node : distributed_nodes_) {
-    node->SetNeedsStyleRecalc(
-        kLocalStyleChange,
-        StyleChangeReasonForTracing::Create(
-            StyleChangeReason::kPropagateInheritChangeToDistributedNodes));
-  }
-}
 
 void HTMLSlotElement::DidRecalcStyle(StyleRecalcChange change) {
-  if (!RuntimeEnabledFeatures::SlotInFlatTreeEnabled())
-    return;
   if (change < kIndependentInherit)
     return;
   for (auto& node : assigned_nodes_) {

third_party/blink/renderer/core/html/html_slot_element.h

@@ -136,7 +136,6 @@ class CORE_EXPORT HTMLSlotElement final : public HTMLElement {
 
   InsertionNotificationRequest InsertedInto(ContainerNode*) final;
   void RemovedFrom(ContainerNode*) final;
-  void WillRecalcStyle(StyleRecalcChange) final;
   void DidRecalcStyle(StyleRecalcChange) final;
 
   void EnqueueSlotChangeEvent();

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -1161,10 +1161,6 @@
     {
       name: "SlimmingPaintV2",
     },
-    {
-      name: "SlotInFlatTree",
-      status: "stable",
-    },
     {
       name: "SMIL",
       status: "stable",