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.

[not at google - send to devlin, 2014/05/20 18:27:12]

This comment is wrong again. It needs to take into account |is_update|. How
about:

If this is a fresh install then |is_update| is false and there must not be any
installed extension with |extension|'s ID. If this is an update then |is_update|
is true and must be an installed extension with |extension|'s ID, and |old_name|
must be non-empty.

[limasdf, 2014/05/21 15:35:08]

Done.

+  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