Remove NOTIFICATION_EXTENSION_ENABLED.

extensions/browser/extension_registry.cc

Index: extensions/browser/extension_registry.cc
diff --git a/extensions/browser/extension_registry.cc b/extensions/browser/extension_registry.cc
index 9c2bf16f53ec80f74192f883ae8753bbd51d8638..69411f36301383cd0b22882591562175ef669980 100644
--- a/extensions/browser/extension_registry.cc
+++ b/extensions/browser/extension_registry.cc
@@ -62,6 +62,13 @@ void ExtensionRegistry::TriggerOnReady(const Extension* extension) {
     observer.OnExtensionReady(browser_context_, extension);
 }
 
+void ExtensionRegistry::TriggerOnEnabled(const Extension* extension) {
+  CHECK(extension);
+  DCHECK(enabled_extensions_.Contains(extension->id()));
+  for (auto& observer : observers_)
+    observer.OnExtensionEnabled(browser_context_, extension);
+}
+
 void ExtensionRegistry::TriggerOnUnloaded(const Extension* extension,
                                           UnloadedExtensionReason reason) {
   CHECK(extension);