Add a counter for ::-webkit-details-marker in stylesheets

This CL has no user-visible behavior changes.

Bug: 590014
Change-Id: I01eeafd34fe9dd02431501d44676e418b547a300
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2262358
Auto-Submit: Kent Tamura <tkent@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781754}

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

@@ -2671,6 +2671,7 @@ enum WebFeature {
   kContentVisibilityHiddenMatchable = 3334,
   kInlineOverflowAutoWithInlineEndPadding = 3335,
   kInlineOverflowScrollWithInlineEndPadding = 3336,
+  kCSSSelectorPseudoWebKitDetailsMarker = 3337,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

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

@@ -58,6 +58,7 @@
 #include "third_party/blink/renderer/core/html/html_slot_element.h"
 #include "third_party/blink/renderer/core/html/media/html_video_element.h"
 #include "third_party/blink/renderer/core/html/parser/html_parser_idioms.h"
+#include "third_party/blink/renderer/core/html/shadow/shadow_element_names.h"
 #include "third_party/blink/renderer/core/html/track/vtt/vtt_element.h"
 #include "third_party/blink/renderer/core/html_names.h"
 #include "third_party/blink/renderer/core/page/focus_controller.h"
@@ -1407,9 +1408,18 @@ bool SelectorChecker::CheckPseudoElement(const SelectorCheckingContext& context,
       }
       return false;
     case CSSSelector::kPseudoWebKitCustomElement: {
-      if (ShadowRoot* root = element.ContainingShadowRoot())
-        return root->IsUserAgent() &&
-               element.ShadowPseudoId() == selector.Value();
+      if (ShadowRoot* root = element.ContainingShadowRoot()) {
+        if (!root->IsUserAgent())
+          return false;
+        if (element.ShadowPseudoId() != selector.Value())
+          return false;
+        if (!is_ua_rule_ &&
+            selector.Value() == shadow_element_names::WebKitDetailsMarker()) {
+          UseCounter::Count(element.GetDocument(),
+                            WebFeature::kCSSSelectorPseudoWebKitDetailsMarker);
+        }
+        return true;
+      }
       return false;
     }
     case CSSSelector::kPseudoBlinkInternalElement:

third_party/blink/renderer/core/html/shadow/details_marker_control.cc

@@ -31,13 +31,14 @@
 #include "third_party/blink/renderer/core/html/shadow/details_marker_control.h"
 
 #include "third_party/blink/renderer/core/html/html_summary_element.h"
+#include "third_party/blink/renderer/core/html/shadow/shadow_element_names.h"
 #include "third_party/blink/renderer/core/layout/layout_details_marker.h"
 
 namespace blink {
 
 DetailsMarkerControl::DetailsMarkerControl(Document& document)
     : HTMLDivElement(document) {
-  SetShadowPseudoId(AtomicString("-webkit-details-marker"));
+  SetShadowPseudoId(shadow_element_names::WebKitDetailsMarker());
 }
 
 LayoutObject* DetailsMarkerControl::CreateLayoutObject(const ComputedStyle&,

third_party/blink/renderer/core/html/shadow/shadow_element_names.cc

@@ -104,6 +104,11 @@ const AtomicString& TextFieldContainer() {
   return name;
 }
 
+const AtomicString& WebKitDetailsMarker() {
+  DEFINE_STATIC_LOCAL(AtomicString, name, ("-webkit-details-marker"));
+  return name;
+}
+
 const AtomicString& FileUploadButton() {
   DEFINE_STATIC_LOCAL(AtomicString, name, ("file-upload-button"));
   return name;

third_party/blink/renderer/core/html/shadow/shadow_element_names.h

@@ -40,6 +40,7 @@ namespace shadow_element_names {
 
 const AtomicString& DetailsContent();
 const AtomicString& DetailsSummary();
+// An ID attribute value for a details marker.
 const AtomicString& DetailsMarker();
 const AtomicString& DateTimeEdit();
 CORE_EXPORT const AtomicString& SpinButton();
@@ -52,6 +53,8 @@ const AtomicString& PasswordRevealButton();
 CORE_EXPORT const AtomicString& SliderThumb();
 const AtomicString& SliderTrack();
 const AtomicString& TextFieldContainer();
+// Pseudo element name ::-webkit-details-marker
+const AtomicString& WebKitDetailsMarker();
 const AtomicString& FileUploadButton();
 const AtomicString& OptGroupLabel();
 

tools/metrics/histograms/enums.xml

@@ -28070,6 +28070,7 @@ Called by update_use_counter_feature_enum.py.-->
   <int value="3334" label="ContentVisibilityHiddenMatchable"/>
   <int value="3335" label="InlineOverflowAutoWithInlineEndPadding"/>
   <int value="3336" label="InlineOverflowScrollWithInlineEndPadding"/>
+  <int value="3337" label="CSSSelectorPseudoWebKitDetailsMarker"/>
 </enum>
 
 <enum name="FeaturePolicyAllowlistType">