Refactoring: de-couple Extensions from "script injection System" [render side]:3

extensions/renderer/injection_host.h

 // Copyright 2015 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 EXTENSIONS_RENDERER_INJECTION_HOST_H
 #define EXTENSIONS_RENDERER_INJECTION_HOST_H
 
 #include "extensions/common/host_id.h"
 #include "extensions/common/permissions/permissions_data.h"
 #include "url/gurl.h"
 
 // An interface for all kinds of hosts who own user scripts.
 class InjectionHost {
  public:
   InjectionHost(const HostID& host_id);
   virtual ~InjectionHost();
 
-  virtual const std::string& GetContentSecurityPolicy() const = 0;
+  virtual std::string GetContentSecurityPolicy() const = 0;
 
   // The base url for the host.
   virtual const GURL& url() const = 0;
 
   // The human-readable name of the host.
   virtual const std::string& name() const = 0;
 
   // Returns true if the script should execute.
   virtual extensions::PermissionsData::AccessType CanExecuteOnFrame(
       const GURL& document_url,
       const GURL& top_frame_url,
       int tab_id,
       bool is_declarative) const = 0;
 
+  // Returns whether the injection host is gone.
+  virtual bool IsGone() const = 0;
+
   const HostID& id() const { return id_; }
  private:
   // The ID of the host.
   HostID id_;
 
   DISALLOW_COPY_AND_ASSIGN(InjectionHost);
 };
 
 #endif  // EXTENSIONS_RENDERER_INJECTION_HOST_H