[Extensions] Propagate activeTab hosts to extension background pages

chrome/renderer/extensions/tab_finder.h

-// 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.
-
-#ifndef CHROME_RENDERER_EXTENSIONS_TAB_FINDER_H_
-#define CHROME_RENDERER_EXTENSIONS_TAB_FINDER_H_
-
-#include "base/basictypes.h"
-#include "base/compiler_specific.h"
-#include "content/public/renderer/render_view_visitor.h"
-
-namespace content {
-class RenderView;
-}
-
-namespace extensions {
-
-// Finds the top RenderView associated with a tab ID.
-class TabFinder : public content::RenderViewVisitor {
- public:
-  // Returns the top RenderView with |tab_id|, or NULL if none is found.
-  static content::RenderView* Find(int tab_id);
-
- private:
-  explicit TabFinder(int tab_id);
-  ~TabFinder() override;
-
-  // content::RenderViewVisitor implementation.
-  bool Visit(content::RenderView* render_view) override;
-
-  int tab_id_;
-  content::RenderView* view_;
-
-  DISALLOW_COPY_AND_ASSIGN(TabFinder);
-};
-
-}  // namespace extensions
-
-#endif  // CHROME_RENDERER_EXTENSIONS_TAB_FINDER_H_