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

chrome/browser/extensions/api/declarative_content/content_action.h

Index: chrome/browser/extensions/api/declarative_content/content_action.h
diff --git a/chrome/browser/extensions/api/declarative_content/content_action.h b/chrome/browser/extensions/api/declarative_content/content_action.h
index dc39431aed870bfe65d677064bf23bc30e542a05..93b2cf79960152f5605f5305041ca874419b9836 100644
--- a/chrome/browser/extensions/api/declarative_content/content_action.h
+++ b/chrome/browser/extensions/api/declarative_content/content_action.h
@@ -95,6 +95,9 @@ 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);
@@ -150,6 +153,13 @@ class RequestContentScript : public ContentAction {
                                      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);