UseCounter: Introduce UseCounter::Observer for layout tests

third_party/WebKit/Source/core/testing/Internals.cpp

Index: third_party/WebKit/Source/core/testing/Internals.cpp
diff --git a/third_party/WebKit/Source/core/testing/Internals.cpp b/third_party/WebKit/Source/core/testing/Internals.cpp
index 45599839a2552add0e97821c0110f42d8927dd66..0a1dc3a9512c80dc54698808fff2ba829b4b09b6 100644
--- a/third_party/WebKit/Source/core/testing/Internals.cpp
+++ b/third_party/WebKit/Source/core/testing/Internals.cpp
@@ -172,6 +172,31 @@ class InternalsIterationSource final
   }
 };
 
+class UseCounterObserverImpl final : public UseCounter::Observer {
+  WTF_MAKE_NONCOPYABLE(UseCounterObserverImpl);
+
+ public:
+  UseCounterObserverImpl(ScriptPromiseResolver* resolver,
+                         UseCounter::Feature feature)
+      : m_resolver(resolver), m_feature(feature) {}
+
+  bool onCountFeature(UseCounter::Feature feature) final {
+    if (m_feature != feature)
+      return false;
+    m_resolver->resolve(feature);
+    return true;
+  }
+
+  DEFINE_INLINE_VIRTUAL_TRACE() {
+    UseCounter::Observer::trace(visitor);
+    visitor->trace(m_resolver);
+  }
+
+ private:
+  Member<ScriptPromiseResolver> m_resolver;
+  UseCounter::Feature m_feature;
+};
+
 }  // namespace
 
 static WTF::Optional<DocumentMarker::MarkerType> markerTypeFrom(
@@ -3009,6 +3034,26 @@ bool Internals::isCSSPropertyUseCounted(Document* document,
   return UseCounter::isCounted(*document, propertyName);
 }
 
+ScriptPromise Internals::observeUseCounter(ScriptState* scriptState,
+                                           Document* document,
+                                           uint32_t feature) {
+  ScriptPromiseResolver* resolver = ScriptPromiseResolver::create(scriptState);
+  ScriptPromise promise = resolver->promise();
+  if (feature >= UseCounter::NumberOfFeatures) {
+    resolver->reject();
+    return promise;
+  }
+  UseCounter::Feature useCounterFeature =
+      static_cast<UseCounter::Feature>(feature);
+  if (UseCounter::isCounted(*document, useCounterFeature)) {
+    resolver->resolve();
+    return promise;
+  }
+  UseCounter::addObserver(
+      *document, new UseCounterObserverImpl(resolver, useCounterFeature));
+  return promise;
+}
+
 String Internals::unscopableAttribute() {
   return "unscopableAttribute";
 }