Take extensions out of Profile into a profile-keyed service, ExtensionSystem.

chrome/browser/extensions/extension_service.h

Index: chrome/browser/extensions/extension_service.h
diff --git a/chrome/browser/extensions/extension_service.h b/chrome/browser/extensions/extension_service.h
index c0905049b4138e763afae4066cb812ba15ff6985..f7e02be8be46620929fdba1f16b5c63c7a635296 100644
--- a/chrome/browser/extensions/extension_service.h
+++ b/chrome/browser/extensions/extension_service.h
@@ -58,6 +58,7 @@ class ExtensionGlobalError;
 class ExtensionManagementEventRouter;
 class ExtensionPreferenceEventRouter;
 class ExtensionSyncData;
+class ExtensionSystem;
 class ExtensionToolbarModel;
 class ExtensionUpdater;
 class ExtensionWebNavigationEventRouter;
@@ -706,9 +707,12 @@ class ExtensionService
 
   NaClModuleInfoList::iterator FindNaClModule(const GURL& url);
 
-  // The profile this ExtensionService is part of.
+  // The normal profile associated with this ExtensionService.
   Profile* profile_;
 
+  // The ExtensionSystem for the profile above.
+  ExtensionSystem* system_;
+
   // Preferences for the owning profile (weak reference).
   ExtensionPrefs* extension_prefs_;