Async Wheel Event with only the first one cancellable behind a flag.

content/public/common/content_features.cc

Index: content/public/common/content_features.cc
diff --git a/content/public/common/content_features.cc b/content/public/common/content_features.cc
index 15fb85f6ab5ca9ed4a15758c954097dfafcf506a..c812eab7c32dd684ee7057ac8fab17e3f6889344 100644
--- a/content/public/common/content_features.cc
+++ b/content/public/common/content_features.cc
@@ -21,6 +21,10 @@ const base::Feature kAllowContentInitiatedDataUrlNavigations{
 const base::Feature kAsmJsToWebAssembly{"AsmJsToWebAssembly",
                                         base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Enables async wheel events.
+const base::Feature kAsyncWheelEvents{"AsyncWheelEvents",
+                                      base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Block subresource requests whose URLs contain embedded credentials (e.g.
 // `https://user:pass@example.com/resource`).
 const base::Feature kBlockCredentialedSubresources{