Add UseCounter for "overflow: overlay"

As the "overflow" shorthand is divided into two longhands: "overflow-x"
and "overflow-y", we add two different counters for both longhands to be
counted while parsing the shorthand.

Bug: 984177
Change-Id: I5eef66b9cc6bc72a023cfeb8b80ac584e71b433e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1724640Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682195}

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

@@ -2360,6 +2360,8 @@ enum WebFeature {
   kToggleEventHandlerDuringParsing = 2978,
   kFragmentDoubleHash = 2979,
   kV8RegExpMatchAllWithNonGlobalRegExp = 2980,
+  kCSSValueOverflowXOverlay = 2981,
+  kCSSValueOverflowYOverlay = 2982,
 
   // 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/parser/css_property_parser_helpers.cc

@@ -1898,6 +1898,14 @@ void CountKeywordOnlyPropertyUsage(CSSPropertyID property,
       if (value_id == CSSValueID::kContents)
         context.Count(WebFeature::kCSSValueDisplayContents);
       break;
+    case CSSPropertyID::kOverflowX:
+      if (value_id == CSSValueID::kOverlay)
+        context.Count(WebFeature::kCSSValueOverflowXOverlay);
+      break;
+    case CSSPropertyID::kOverflowY:
+      if (value_id == CSSValueID::kOverlay)
+        context.Count(WebFeature::kCSSValueOverflowYOverlay);
+      break;
     default:
       break;
   }

tools/metrics/histograms/enums.xml

@@ -24152,6 +24152,8 @@ Called by update_net_error_codes.py.-->
   <int value="2978" label="ToggleEventHandlerDuringParsing"/>
   <int value="2979" label="FragmentDoubleHash"/>
   <int value="2980" label="V8RegExpMatchAllWithNonGlobalRegExp"/>
+  <int value="2981" label="CSSValueOverflowXOverlay"/>
+  <int value="2982" label="CSSValueOverflowYOverlay"/>
 </enum>
 
 <enum name="FeaturePolicyAllowlistType">