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

content/public/common/content_features.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "build/build_config.h"
 #include "content/public/common/content_features.h"
 
 namespace features {
 
 // All features in alphabetical order.
 
 // Enables content-initiated, main frame navigations to data URLs.
 // TODO(meacer): Remove when the deprecation is complete.
 //               https://www.chromestatus.com/feature/5669602927312896
 const base::Feature kAllowContentInitiatedDataUrlNavigations{
     "AllowContentInitiatedDataUrlNavigations",
     base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enables asm.js to WebAssembly V8 backend.
 // http://asmjs.org/spec/latest/
 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{
     "BlockCredentialedSubresources", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enables brotli "Accept-Encoding" advertising and "Content-Encoding" support.
 // Brotli format specification: http://www.ietf.org/id/draft-alakuijala-brotli
 const base::Feature kBrotliEncoding{"brotli-encoding",
                                     base::FEATURE_ENABLED_BY_DEFAULT};
 
@@ skipping 339 matching lines @@
 #endif
 
 #if defined(OS_WIN)
 // Emergency "off switch" for new Windows sandbox security mitigation,
 // sandbox::MITIGATION_EXTENSION_POINT_DISABLE.
 const base::Feature kWinSboxDisableExtensionPoints{
     "WinSboxDisableExtensionPoint", base::FEATURE_ENABLED_BY_DEFAULT};
 #endif
 
 }  // namespace features