UMA for measuring how often 2 or more tabs script the same background contents.

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 <string>
@@ skipping 517 matching lines @@
   if (pending_render_frame_host_ &&
       pending_render_frame_host_->GetSiteInstance() != source_site_instance) {
     pending_render_frame_host_->UpdateOpener();
   }
 
   if (speculative_render_frame_host_ &&
       speculative_render_frame_host_->GetSiteInstance() !=
           source_site_instance) {
     speculative_render_frame_host_->UpdateOpener();
   }
+
+  frame_tree_node_->current_frame_host()->delegate()->DidChangeOpener(
+      frame_tree_node_, opener);
 }
 
 void RenderFrameHostManager::CommitPendingFramePolicy() {
   // Return early if there were no pending updates to sandbox flags or container
   // policy.
   if (!frame_tree_node_->CommitPendingFramePolicy())
     return;
 
   // Policy updates can only happen when the frame has a parent.
   CHECK(frame_tree_node_->parent());
@@ skipping 2306 matching lines @@
           delegate_->IsHidden()) {
     if (delegate_->IsHidden()) {
       render_frame_host_->GetView()->Hide();
     } else {
       render_frame_host_->GetView()->Show();
     }
   }
 }
 
 }  // namespace content