[Reland] Allow headless TabSocket in isolated worlds & remove obsolete logic

headless/lib/renderer/headless_content_renderer_client.h

 // Copyright 2017 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.
 
 #ifndef HEADLESS_LIB_RENDERER_HEADLESS_CONTENT_RENDERER_CLIENT_H_
 #define HEADLESS_LIB_RENDERER_HEADLESS_CONTENT_RENDERER_CLIENT_H_
 
 #include "content/public/renderer/content_renderer_client.h"
 
 namespace headless {
 
 class HeadlessContentRendererClient : public content::ContentRendererClient {
  public:
   HeadlessContentRendererClient();
   ~HeadlessContentRendererClient() override;
 
  private:
   void RenderFrameCreated(content::RenderFrame* render_frame) override;
-  void RunScriptsAtDocumentStart(content::RenderFrame* render_frame) override;
 
   DISALLOW_COPY_AND_ASSIGN(HeadlessContentRendererClient);
 };
 
 }  // namespace headless
 
 #endif  // HEADLESS_LIB_RENDERER_HEADLESS_CONTENT_RENDERER_CLIENT_H_