Adding an experimental app notification API.

content/common/notification_type.h

Index: content/common/notification_type.h
diff --git a/content/common/notification_type.h b/content/common/notification_type.h
index 50e6f762cb7c3894a31e33dbaf095c2c3fa71fef..7e8dfe01022f956ed773134460f74c5f40f3b4ad 100644
--- a/content/common/notification_type.h
+++ b/content/common/notification_type.h
@@ -982,6 +982,11 @@ class NotificationType {
     // (const std::string).
     EXTENSION_UPDATE_FOUND,
 
+    // An installed app changed notification state (added or removed
+    // notifications). The source is a Profile, and the details are a string
+    // with the extension id of the app.
+    APP_NOTIFICATION_STATE_CHANGED,
+
     // Desktop Notifications ---------------------------------------------------
 
     // This notification is sent when a balloon is connected to a renderer