DO NOT COMMIT: Revert "Enable subframe FrameNavigationEntries by default."

content/common/site_isolation_policy.cc

Index: content/common/site_isolation_policy.cc
diff --git a/content/common/site_isolation_policy.cc b/content/common/site_isolation_policy.cc
index 4ab845d60b23daaf0c442a96127e2e060ad46ff6..77ac24a30e8dd33bcb1bfdb4fd3df73e415cad6f 100644
--- a/content/common/site_isolation_policy.cc
+++ b/content/common/site_isolation_policy.cc
@@ -39,7 +39,10 @@ bool SiteIsolationPolicy::IsTopDocumentIsolationEnabled() {
 
 // static
 bool SiteIsolationPolicy::UseSubframeNavigationEntries() {
-  return true;
+  // Enable the new navigation history behavior if any manner of site isolation
+  // is active.
+  // PlzNavigate: also enable the new navigation history behavior.
+  return AreCrossProcessFramesPossible() || IsBrowserSideNavigationEnabled();
 }
 
 }  // namespace content