Enforce all subframes to be in the same BrowsingInstance as the parent.

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 <algorithm>
 #include <utility>
 
 #include "base/command_line.h"
@@ skipping 1251 matching lines @@
          !base::CommandLine::ForCurrentProcess()->HasSwitch(
              switches::kProcessPerTab);
 }
 
 bool RenderFrameHostManager::ShouldSwapBrowsingInstancesForNavigation(
     const GURL& current_effective_url,
     bool current_is_view_source_mode,
     SiteInstance* new_site_instance,
     const GURL& new_effective_url,
     bool new_is_view_source_mode) const {
+  // A subframe must stay in the same BrowsingInstance as its parent.
+  // TODO(nasko): Ensure that SiteInstance swap is still triggered for subframes
+  // in the cases covered by the rest of the checks in this method.
+  if (!frame_tree_node_->IsMainFrame())
+    return false;
+
   // If new_entry already has a SiteInstance, assume it is correct.  We only
   // need to force a swap if it is in a different BrowsingInstance.
   if (new_site_instance) {
     return !new_site_instance->IsRelatedSiteInstance(
         render_frame_host_->GetSiteInstance());
   }
 
   // Check for reasons to swap processes even if we are in a process model that
   // doesn't usually swap (e.g., process-per-tab).  Any time we return true,
   // the new_entry will be rendered in a new SiteInstance AND BrowsingInstance.
@@ skipping 1373 matching lines @@
 int RenderFrameHostManager::GetOpenerRoutingID(SiteInstance* instance) {
   if (!frame_tree_node_->opener())
     return MSG_ROUTING_NONE;
 
   return frame_tree_node_->opener()
       ->render_manager()
       ->GetRoutingIdForSiteInstance(instance);
 }
 
 }  // namespace content