ElementInternals: Implement disabledFeatures=['shadow']

Add support of disabledFeatures=['shadow'] in a custom element
definition. It disables Element.attachShadow().

Specification PR: https://github.com/whatwg/dom/pull/760
The behavior is behind "ElemnetInternals" runtime flag.

Bug: 905922
Change-Id: Ib950883b5c995945eb60bf9b92c715ad3996dfa4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1609022
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Hayato Ito <hayato@chromium.org>
Reviewed-by: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661327}

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

@@ -2892,6 +2892,23 @@ ShadowRoot* Element::attachShadow(const ShadowRootInit* shadow_root_init_dict,
     return nullptr;
   }
 
+  // Checking IsCustomElement() here is just an optimization because
+  // IsValidName() is not cheap.
+  if (RuntimeEnabledFeatures::ElementInternalsEnabled() && IsCustomElement() &&
+      (CustomElement::IsValidName(localName()) || !IsValue().IsNull())) {
+    auto* registry = CustomElement::Registry(*this);
+    auto* definition =
+        registry ? registry->DefinitionForName(IsValue().IsNull() ? localName()
+                                                                  : IsValue())
+                 : nullptr;
+    if (definition && definition->DisableShadow()) {
+      exception_state.ThrowDOMException(
+          DOMExceptionCode::kNotSupportedError,
+          "attachShadow() is disabled by disabledFeatures static field.");
+      return nullptr;
+    }
+  }
+
   if (GetShadowRoot()) {
     exception_state.ThrowDOMException(DOMExceptionCode::kNotSupportedError,
                                       "Shadow root cannot be created on a host "

third_party/blink/renderer/core/html/custom/custom_element_definition.cc

@@ -34,6 +34,7 @@ CustomElementDefinition::CustomElementDefinition(
       observed_attributes_(observed_attributes),
       has_style_attribute_changed_callback_(
           observed_attributes.Contains(html_names::kStyleAttr.LocalName())),
+      disable_shadow_(disabled_features.Contains(String("shadow"))),
       disable_internals_(disabled_features.Contains(String("internals"))),
       is_form_associated_(form_association_flag == FormAssociationFlag::kYes) {}
 

third_party/blink/renderer/core/html/custom/custom_element_definition.h

@@ -122,6 +122,7 @@ class CORE_EXPORT CustomElementDefinition
   bool HasDefaultStyleSheets() const {
     return !default_style_sheets_.IsEmpty();
   }
+  bool DisableShadow() const { return disable_shadow_; }
   bool DisableInternals() const { return disable_internals_; }
   bool IsFormAssociated() const { return is_form_associated_; }
 
@@ -162,6 +163,7 @@ class CORE_EXPORT CustomElementDefinition
   HashSet<AtomicString> observed_attributes_;
   bool has_style_attribute_changed_callback_;
   bool added_default_style_sheet_ = false;
+  bool disable_shadow_ = false;
   bool disable_internals_ = false;
   bool is_form_associated_ = false;
 

third_party/blink/web_tests/external/wpt/shadow-dom/Element-interface-attachShadow-custom-element-expected.txt

-This is a testharness.js-based test.
-PASS Element.attachShadow must create an instance of ShadowRoot for autonomous custom elements
-PASS Element.attachShadow must create an instance of ShadowRoot for undefined autonomous custom elements
-FAIL Element.attachShadow for an autonomous custom element with disabledFeatures=["shadow"] should throw a NotSupportedError assert_throws: Definition, not a host function "() => {
-    document.createElement('shadow-disabled-element').attachShadow({mode: 'closed'});
-  }" did not throw
-FAIL Element.attachShadow for a customized built-in element with disabledFeatures=["shadow"] should throw a NotSupportedError assert_throws: Definition, not a host function "() => {
-    h2.attachShadow({mode: 'closed'});
-  }" did not throw
-PASS Element.attachShadow for a custom element with disabledFeatures=["SHADOW"] should not throw a NotSupportedError
-PASS Element.attachShadow must throw a NotSupportedError for customized built-in elements
-Harness: the test ran to completion.
-