Revert of Disable support for swapped out RenderFrame(Host)

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/content_client.h"
 #include "content/public/common/content_switches.h"
@@ skipping 55 matching lines @@
 
 // static
 bool SiteIsolationPolicy::UseSubframeNavigationEntries() {
   // Enable the new navigation history behavior if any manner of site isolation
   // is active.
   return AreCrossProcessFramesPossible();
 }
 
 // static
 bool SiteIsolationPolicy::IsSwappedOutStateForbidden() {
-  return true;
+  return AreCrossProcessFramesPossible();
 }
 
 // static
 bool SiteIsolationPolicy::IsolateAllSitesForTesting() {
   // TODO(nick): Re-enable once https://crbug.com/133403 is fixed.
   // if (!(g_site_isolation_whitelist == nullptr)) return false;
   base::CommandLine::ForCurrentProcess()->AppendSwitch(
       switches::kSitePerProcess);
   return true;
 }
 
 }  // namespace content