Add a function triggering extension installed to ExtensionRegistryObserver

extensions/browser/extension_registry_observer.h

Index: extensions/browser/extension_registry_observer.h
diff --git a/extensions/browser/extension_registry_observer.h b/extensions/browser/extension_registry_observer.h
index 5880add25e63307af4691dae2e4bc98bdbcd7b99..b030e5af9c437722330ad7d1b7b46702083dada2 100644
--- a/extensions/browser/extension_registry_observer.h
+++ b/extensions/browser/extension_registry_observer.h
@@ -33,6 +33,17 @@ class ExtensionRegistryObserver {
   virtual void OnExtensionUnloaded(content::BrowserContext* browser_context,
                                    const Extension* extension,
                                    UnloadedExtensionInfo::Reason reason) {}
+
+  // Called an extension is about to finish install. The extension won't be in

[not at google - send to devlin, 2014/05/16 23:03:35]

Thanks for adding the comment. How about a slight variation:

Called when |extension| is about to be installed. |is_update| is true if the
installation is the result of it updating, in which case |old_name| is the name
of the extension's previous version.

The ExtensionRegistry will not be tracking |extension| at the time this event is
fired, but will be immediately afterwards (note: not necessarily enabled; it
might be installed in the disabled or even blacklisted sets, for example).

Note that it's much more common to care about extensions being loaded
(OnExtensionLoaded).

[limasdf, 2014/05/17 06:16:19]

Done. Thank you.

+  // ExtensionRegistry and about to appear in the ExtensionRegistry.
+  // (But could be in any of the sets(terminated, blacklisted, enabled ,.).
+  // Caller probably want to listen for |OnExtensionLoaded()| unless they really
+  // want to know when an extension is about to be installed.
+  virtual void OnExtensionWillBeInstalled(
+      content::BrowserContext* browser_context,
+      const Extension* extension,
+      bool is_update,
+      const std::string& old_name) {}
 };
 
 }  // namespace extensions