Add FeatureList plumbing for the LazyParseCSS experiment

content/child/runtime_features.cc

Index: content/child/runtime_features.cc
diff --git a/content/child/runtime_features.cc b/content/child/runtime_features.cc
index 2698bf32ae15ff7f5d97eb0f07acad7f861612f9..e26853c24bd3f9386bb610bb7fc3b84caccade9b 100644
--- a/content/child/runtime_features.cc
+++ b/content/child/runtime_features.cc
@@ -248,6 +248,9 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
   if (base::FeatureList::IsEnabled(features::kDocumentWriteEvaluator))
     WebRuntimeFeatures::enableDocumentWriteEvaluator(true);
 
+  if (base::FeatureList::IsEnabled(features::kLazyParseCSS))
+    WebRuntimeFeatures::enableLazyParseCSS(true);
+
   WebRuntimeFeatures::enableMediaDocumentDownloadButton(
       base::FeatureList::IsEnabled(features::kMediaDocumentDownloadButton));