Main frame's unique name can always be null.

content/browser/web_contents/web_contents_impl.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 "content/browser/web_contents/web_contents_impl.h"
 
 #include <stddef.h>
 
 #include <cmath>
 #include <utility>
@@ skipping 1520 matching lines @@
   int32_t main_frame_widget_routing_id = params.main_frame_widget_routing_id;
   if (main_frame_widget_routing_id == MSG_ROUTING_NONE) {
     view_routing_id = main_frame_widget_routing_id =
         site_instance->GetProcess()->GetNextRoutingID();
   }
 
   GetRenderManager()->Init(site_instance.get(), view_routing_id,
                            params.main_frame_routing_id,
                            main_frame_widget_routing_id);
 
-  // blink::FrameTree::setName uses |name| as the |unique_name| for the main
-  // frame - let's do the same thing here.
-  std::string unique_name = params.main_frame_name;
+  // blink::FrameTree::setName always keeps |unique_name| empty in case of a
+  // main frame - let's do the same thing here.
+  std::string unique_name;
   frame_tree_.root()->SetFrameName(params.main_frame_name, unique_name);
 
   WebContentsViewDelegate* delegate =
       GetContentClient()->browser()->GetWebContentsViewDelegate(this);
 
 #if defined(USE_AURA)
   if (MojoShellConnection::GetForProcess() &&
       base::CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kUseMusInRenderer)) {
     ui::Window* mus_window = aura::GetMusWindow(params.context);
@@ skipping 3651 matching lines @@
   for (RenderViewHost* render_view_host : render_view_host_set)
     render_view_host->OnWebkitPreferencesChanged();
 }
 
 void WebContentsImpl::SetJavaScriptDialogManagerForTesting(
     JavaScriptDialogManager* dialog_manager) {
   dialog_manager_ = dialog_manager;
 }
 
 }  // namespace content