Ship the ancestor restriction to 'first-party'.

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 84b04d9fcf18517c3e277134cf1f6f9e12203036..978305a05dc26d2d592d90fbfc4f9813a7cf8e62 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -4001,9 +4001,6 @@ String Document::lastModified() const
 
 const KURL& Document::firstPartyForCookies() const
 {
-    if (!RuntimeEnabledFeatures::firstPartyIncludesAncestorsEnabled())
-        return topDocument().url();
-
     // We're intentionally using the URL of each document rather than the document's SecurityOrigin.
     // Sandboxing a document into a unique origin shouldn't effect first-/third-party status for
     // cookies and site data.