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

content/common/site_isolation_policy.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 "content/common/site_isolation_policy.h"
 
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
 #include "content/public/common/browser_side_navigation_policy.h"
 #include "content/public/common/content_client.h"
@@ skipping 21 matching lines @@
   // --site-per-process trumps --top-document-isolation.
   if (UseDedicatedProcessesForAllSites())
     return false;
 
   return base::CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kTopDocumentIsolation);
 }
 
 // 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