Remove LayoutNGFieldset runtime flag

The flag has been enabled since M86, and we have never seen regression
issues recently.

This CL has no behavior changes.

Change-Id: I886c8c0263667fb60c960981a1c36a67d06cba53
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2711745
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Auto-Submit: Kent Tamura <tkent@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#857006}

third_party/blink/public/mojom/web_feature/web_feature.mojom

@@ -2535,7 +2535,6 @@ enum WebFeature {
   kLegacyLayoutByDeprecatedFlexBox = 3205,
   kLegacyLayoutByDetailsMarker = 3206,
   kLegacyLayoutByEditing = 3207,
-  kLegacyLayoutByFieldSet = 3208,
   kLegacyLayoutByFlexBox = 3210,
   kLegacyLayoutByFrameSet = 3211,
   kLegacyLayoutByGrid = 3212,

third_party/blink/renderer/core/html/forms/html_field_set_element.cc

@@ -135,10 +135,6 @@ LayoutBox* HTMLFieldSetElement::GetLayoutBoxForScrolling() const {
   return HTMLFormControlElement::GetLayoutBoxForScrolling();
 }
 
-bool HTMLFieldSetElement::TypeShouldForceLegacyLayout() const {
-  return !RuntimeEnabledFeatures::LayoutNGFieldsetEnabled();
-}
-
 HTMLLegendElement* HTMLFieldSetElement::Legend() const {
   return Traversal<HTMLLegendElement>::FirstChild(*this);
 }

third_party/blink/renderer/core/html/forms/html_field_set_element.h

@@ -48,7 +48,6 @@ class CORE_EXPORT HTMLFieldSetElement final : public HTMLFormControlElement {
   bool SupportsFocus() const override;
   LayoutObject* CreateLayoutObject(const ComputedStyle&, LegacyLayout) override;
   LayoutBox* GetLayoutBoxForScrolling() const override;
-  bool TypeShouldForceLegacyLayout() const final;
   const AtomicString& FormControlType() const override;
   bool RecalcWillValidate() const override { return false; }
   bool MatchesValidityPseudoClasses() const final;

third_party/blink/renderer/core/layout/layout_block.cc

@@ -1064,9 +1064,7 @@ void LayoutBlock::RemovePositionedObject(LayoutBox* o) {
 
 bool LayoutBlock::IsAnonymousNGFieldsetContentWrapper() const {
   NOT_DESTROYED();
-  if (!RuntimeEnabledFeatures::LayoutNGFieldsetEnabled() || !Parent())
-    return false;
-  return Parent()->IsLayoutNGFieldset();
+  return Parent() && Parent()->IsLayoutNGFieldset();
 }
 
 void LayoutBlock::InvalidatePaint(

third_party/blink/renderer/core/layout/layout_fieldset.cc

@@ -145,18 +145,16 @@ LayoutObject* LayoutFieldset::LayoutSpecialExcludedChild(bool relayout_children,
 LayoutBox* LayoutFieldset::FindInFlowLegend(const LayoutBlock& fieldset) {
   DCHECK(fieldset.IsFieldset() || fieldset.IsLayoutNGFieldset());
   const LayoutBlock* parent = &fieldset;
-  if (RuntimeEnabledFeatures::LayoutNGFieldsetEnabled()) {
-    if (fieldset.IsLayoutNGFieldset()) {
-      // If there is a rendered legend, it will be found inside the anonymous
-      // fieldset wrapper.
-      parent = To<LayoutBlock>(fieldset.FirstChild());
-      if (!parent)
-        return nullptr;
-      // If the anonymous fieldset wrapper is a multi-column, the rendered
-      // legend will be found inside the multi-column flow thread.
-      if (parent->FirstChild() && parent->FirstChild()->IsLayoutFlowThread())
-        parent = To<LayoutBlock>(parent->FirstChild());
-    }
+  if (fieldset.IsLayoutNGFieldset()) {
+    // If there is a rendered legend, it will be found inside the anonymous
+    // fieldset wrapper.
+    parent = To<LayoutBlock>(fieldset.FirstChild());
+    if (!parent)
+      return nullptr;
+    // If the anonymous fieldset wrapper is a multi-column, the rendered
+    // legend will be found inside the multi-column flow thread.
+    if (parent->FirstChild() && parent->FirstChild()->IsLayoutFlowThread())
+      parent = To<LayoutBlock>(parent->FirstChild());
   }
   for (LayoutObject* legend = parent->FirstChild(); legend;
        legend = legend->NextSibling()) {

third_party/blink/renderer/core/layout/layout_object.cc

@@ -610,15 +610,15 @@ bool LayoutObject::IsRenderedLegendInternal() const {
   // We may not be inserted into the tree yet.
   if (!parent)
     return false;
-  if (RuntimeEnabledFeatures::LayoutNGFieldsetEnabled()) {
-    // If there is a rendered legend, it will be found inside the anonymous
-    // fieldset wrapper. If the anonymous fieldset wrapper is a multi-column,
-    // the rendered legend will be found inside the multi-column flow thread.
-    if (parent->IsLayoutFlowThread())
-      parent = parent->Parent();
-    if (parent->IsAnonymous() && parent->Parent()->IsLayoutNGFieldset())
-      parent = parent->Parent();
-  }
+
+  // If there is a rendered legend, it will be found inside the anonymous
+  // fieldset wrapper. If the anonymous fieldset wrapper is a multi-column,
+  // the rendered legend will be found inside the multi-column flow thread.
+  if (parent->IsLayoutFlowThread())
+    parent = parent->Parent();
+  if (parent->IsAnonymous() && parent->Parent()->IsLayoutNGFieldset())
+    parent = parent->Parent();
+
   const auto* parent_layout_block = DynamicTo<LayoutBlock>(parent);
   return parent_layout_block && IsA<HTMLFieldSetElement>(parent->GetNode()) &&
          LayoutFieldset::FindInFlowLegend(*parent_layout_block) == this;

third_party/blink/renderer/core/layout/layout_object_factory.cc

@@ -250,11 +250,8 @@ LayoutObject* LayoutObjectFactory::CreateButton(Node& node,
 LayoutBlock* LayoutObjectFactory::CreateFieldset(Node& node,
                                                  const ComputedStyle& style,
                                                  LegacyLayout legacy) {
-  bool disable_ng_for_type = !RuntimeEnabledFeatures::LayoutNGFieldsetEnabled();
-  if (disable_ng_for_type)
-    UseCounter::Count(node.GetDocument(), WebFeature::kLegacyLayoutByFieldSet);
   return CreateObject<LayoutBlock, LayoutNGFieldset, LayoutFieldset>(
-      node, style, legacy, disable_ng_for_type);
+      node, style, legacy);
 }
 
 LayoutBlockFlow* LayoutObjectFactory::CreateFileUploadControl(

third_party/blink/renderer/core/layout/ng/ng_fieldset_layout_algorithm_test.cc

@@ -15,12 +15,10 @@ namespace {
 
 class NGFieldsetLayoutAlgorithmTest
     : public NGBaseLayoutAlgorithmTest,
-      private ScopedLayoutNGFieldsetForTest,
       private ScopedLayoutNGBlockFragmentationForTest {
  protected:
   NGFieldsetLayoutAlgorithmTest()
-      : ScopedLayoutNGFieldsetForTest(true),
-        ScopedLayoutNGBlockFragmentationForTest(true) {}
+      : ScopedLayoutNGBlockFragmentationForTest(true) {}
 
   scoped_refptr<const NGPhysicalBoxFragment> RunBlockLayoutAlgorithm(
       Element* element) {

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -1140,11 +1140,6 @@
       name: "LayoutNGBlockFragmentation",
       implied_by: ["LayoutNGPrinting"],
     },
-    {
-      name: "LayoutNGFieldset",
-      depends_on: ["LayoutNG"],
-      status: "stable",
-    },
     {
       // Traverse the fragment tree when painting and hit-testing, instead of
       // the layout object tree.

tools/metrics/histograms/enums.xml

@@ -30961,7 +30961,7 @@ Called by update_use_counter_feature_enum.py.-->
   <int value="3205" label="LegacyLayoutByDeprecatedFlexBox"/>
   <int value="3206" label="LegacyLayoutByDetailsMarker"/>
   <int value="3207" label="LegacyLayoutByEditing"/>
-  <int value="3208" label="LegacyLayoutByFieldSet"/>
+  <int value="3208" label="OBSOLETE_LegacyLayoutByFieldSet"/>
   <int value="3209" label="OBSOLETE_LegacyLayoutByFileUploadControl"/>
   <int value="3210" label="LegacyLayoutByFlexBox"/>
   <int value="3211" label="LegacyLayoutByFrameSet"/>