Introduce HostID and de-couple Extensions from "script injection System" [browser side]

chrome/browser/extensions/api/declarative_content/content_action.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_BROWSER_EXTENSIONS_API_DECLARATIVE_CONTENT_CONTENT_ACTION_H_
 #define CHROME_BROWSER_EXTENSIONS_API_DECLARATIVE_CONTENT_CONTENT_ACTION_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 77 matching lines @@
  protected:
   friend class base::RefCounted<ContentAction>;
   virtual ~ContentAction();
 };
 
 // Action that injects a content script.
 class RequestContentScript : public ContentAction {
  public:
   struct ScriptData;
 
+  // TODO(hanxi): add RulesRegistryID to the RequestKey.
+  using RequestKey = std::string;
+
   RequestContentScript(content::BrowserContext* browser_context,
                        const Extension* extension,
                        const ScriptData& script_data);
   RequestContentScript(DeclarativeUserScriptMaster* master,
                        const Extension* extension,
                        const ScriptData& script_data);
 
   static scoped_refptr<ContentAction> Create(
       content::BrowserContext* browser_context,
       const Extension* extension,
@@ skipping 35 matching lines @@
     DCHECK(master_);
     master_->AddScript(script_);
   }
 
   ~RequestContentScript() override;
 
   void InstructRenderProcessToInject(content::WebContents* contents,
                                      const std::string& extension_id) const;
 
   UserScript script_;
+
+  // The lifetime of the |master_| is managed by DeclarativeUserScriptManager,

[Devlin, 2015/01/21 23:25:20]

How about instead
"Since the lifetime of DeclarativeUserScriptMasters is managed by the
ExtensionSystem, it is safe to use a raw pointer (as all extension APIs
have a dependency on the system)."

[Xi Han, 2015/01/22 17:19:36]

Sounds better, thanks!

+  // which manages a map of master objects.
+  // DeclarativeUserScriptManager is owned by ExtensionSystemImpl::Shared, and a
+  // master object will only be desctructed when the
+  // DeclarativeUserScriptManager is desctructed.
+  // So it is safe to use a raw pointer here.
   DeclarativeUserScriptMaster* master_;
 
   DISALLOW_COPY_AND_ASSIGN(RequestContentScript);
 };
 
 typedef DeclarativeActionSet<ContentAction> ContentActionSet;
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_DECLARATIVE_CONTENT_CONTENT_ACTION_H_