Don't split off NTP subframes with TDI.

content/browser/frame_host/render_frame_host_manager.cc

 // Copyright 2013 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/browser/frame_host/render_frame_host_manager.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <utility>
@@ skipping 1418 matching lines @@
           frame_tree_node_->opener()->current_frame_host();
       if (IsCurrentlySameSite(opener_frame, dest_url))
         return SiteInstanceDescriptor(opener_frame->GetSiteInstance());
     }
   }
 
   if (!frame_tree_node_->IsMainFrame() &&
       SiteIsolationPolicy::IsTopDocumentIsolationEnabled() &&
       !SiteInstanceImpl::DoesSiteRequireDedicatedProcess(browser_context,
                                                          dest_url)) {
+    if (GetContentClient()
+            ->browser()
+            ->ShouldFrameShareParentSiteInstanceDespiteTopDocumentIsolation(
+                dest_url, current_instance)) {
+      return SiteInstanceDescriptor(render_frame_host_->GetSiteInstance());
+    }
+
     // This is a cross-site subframe of a non-isolated origin, so place this
     // frame in the default subframe site instance.
     return SiteInstanceDescriptor(
         browser_context, dest_url,
         SiteInstanceRelation::RELATED_DEFAULT_SUBFRAME);
   }
 
   // Start the new renderer in a new SiteInstance, but in the current
   // BrowsingInstance.
   return SiteInstanceDescriptor(browser_context, dest_url,
@@ skipping 1273 matching lines @@
                                              resolved_url)) {
     DCHECK(!dest_instance ||
            dest_instance == render_frame_host_->GetSiteInstance());
     return false;
   }
 
   return true;
 }
 
 }  // namespace content