New WebContents created via ctrl-click should be in a new process.

chrome/browser/extensions/api/tabs/tabs_api.cc

 // Copyright (c) 2012 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 "chrome/browser/extensions/api/tabs/tabs_api.h"
 
 #include <stddef.h>
 #include <algorithm>
 #include <limits>
 #include <memory>
@@ skipping 603 matching lines @@
     create_params.initial_show_state =
         ConvertToWindowShowState(create_data->state);
   }
 
   Browser* new_window = new Browser(create_params);
 
   for (const GURL& url : urls) {
     chrome::NavigateParams navigate_params(new_window, url,
                                            ui::PAGE_TRANSITION_LINK);
     navigate_params.disposition = WindowOpenDisposition::NEW_FOREGROUND_TAB;
+
+    // The next 2 statements put the new contents in the same BrowsingInstance
+    // as their opener.  Note that |force_new_process_for_new_contents = false|
+    // means that new contents might still end up in a new renderer
+    // (if they open a web URL and are transferred out of an extension
+    // renderer), but even in this case the flags below ensure findability via
+    // window.open.
+    navigate_params.force_new_process_for_new_contents = false;
     navigate_params.source_site_instance =
         render_frame_host()->GetSiteInstance();
+
     chrome::Navigate(&navigate_params);
   }
 
   WebContents* contents = NULL;
   // Move the tab into the created window only if it's an empty popup or it's
   // a tabbed window.
   if ((window_type == Browser::TYPE_POPUP && urls.empty()) ||
       window_type == Browser::TYPE_TABBED) {
     if (source_tab_strip)
       contents = source_tab_strip->DetachWebContentsAt(tab_index);
@@ skipping 1500 matching lines @@
       params->tab_id
           ? ErrorUtils::FormatErrorMessage(keys::kCannotDiscardTab,
                                            base::IntToString(*params->tab_id))
           : keys::kCannotFindTabToDiscard));
 }
 
 TabsDiscardFunction::TabsDiscardFunction() {}
 TabsDiscardFunction::~TabsDiscardFunction() {}
 
 }  // namespace extensions