Extract DeclarativeUserScriptManager from ExtensionSystem.

extensions/browser/extension_system.h

Index: extensions/browser/extension_system.h
diff --git a/extensions/browser/extension_system.h b/extensions/browser/extension_system.h
index e5dd4680033c715d0feeb1f01c861fe38908d2bf..4e1c73dcdf4a172e45409c37eba6ab465fe38f4e 100644
--- a/extensions/browser/extension_system.h
+++ b/extensions/browser/extension_system.h
@@ -30,7 +30,6 @@ class BrowserContext;
 namespace extensions {
 
 class ContentVerifier;
-class DeclarativeUserScriptManager;
 class EventRouter;
 class Extension;
 class ExtensionSet;
@@ -76,9 +75,6 @@ class ExtensionSystem : public KeyedService {
   // The SharedUserScriptMaster is created at startup.
   virtual SharedUserScriptMaster* shared_user_script_master() = 0;
 
-  // The DeclarativeUserScriptManager is created at startup.
-  virtual DeclarativeUserScriptManager* declarative_user_script_manager() = 0;
-
   // The StateStore is created at startup.
   virtual StateStore* state_store() = 0;