Update ScopedObserver declarations (mostly Chrome OS specific)

This allows the chrome target to compile on CrOS with the
ScopedObserver changes.

Bug: 998625
Change-Id: I5907d0d1910c616ba72dfc887e8ee1c0188ca56b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1842672
Commit-Queue: Evan Stade <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Cr-Commit-Position: refs/heads/master@{#704273}
diff --git a/chrome/browser/supervised_user/supervised_user_service.h b/chrome/browser/supervised_user/supervised_user_service.h
index a184057..f4582648 100644
--- a/chrome/browser/supervised_user/supervised_user_service.h
+++ b/chrome/browser/supervised_user/supervised_user_service.h
@@ -30,6 +30,7 @@
 #include "extensions/buildflags/buildflags.h"
 
 #if BUILDFLAG(ENABLE_EXTENSIONS)
+#include "extensions/browser/extension_registry.h"
 #include "extensions/browser/extension_registry_observer.h"
 #include "extensions/browser/management_policy.h"
 #endif
@@ -48,10 +49,6 @@
 class Version;
 }
 
-namespace extensions {
-class ExtensionRegistry;
-}
-
 namespace user_prefs {
 class PrefRegistrySyncable;
 }
@@ -339,7 +336,7 @@
 #if BUILDFLAG(ENABLE_EXTENSIONS)
   ScopedObserver<extensions::ExtensionRegistry,
                  extensions::ExtensionRegistryObserver>
-      registry_observer_;
+      registry_observer_{this};
 #endif
 
   base::ObserverList<SupervisedUserServiceObserver>::Unchecked observer_list_;