Add a function triggering extension installed to ExtensionRegistryObserver

extensions/browser/extension_registry.h

Index: extensions/browser/extension_registry.h
diff --git a/extensions/browser/extension_registry.h b/extensions/browser/extension_registry.h
index d8df24b3653d51b30a7b5996ae96579442d832a9..66208404eec4c4ded301be406cd2ffa67e9c19c5 100644
--- a/extensions/browser/extension_registry.h
+++ b/extensions/browser/extension_registry.h
@@ -74,6 +74,13 @@ class ExtensionRegistry : public KeyedService {
   void TriggerOnUnloaded(const Extension* extension,
                          UnloadedExtensionInfo::Reason reason);
 
+  // Invokes the observer method OnExtensionWillBeInstalled(). The extension
+  // must not be tracked at the time of the call, and the caller should ensure
+  // to track it afterward.
+  void TriggerOnWillBeInstalled(const Extension* extension,
+                                bool is_update,
+                                const std::string& old_name);
+
   // Find an extension by ID using |include_mask| to pick the sets to search:
   //  * enabled_extensions()     --> ExtensionRegistry::ENABLED
   //  * disabled_extensions()    --> ExtensionRegistry::DISABLED