Allow extension APIs to be called from WebUI.

extensions/common/features/feature.h

Index: extensions/common/features/feature.h
diff --git a/extensions/common/features/feature.h b/extensions/common/features/feature.h
index 37387d7491959be4001f133ee69e882d4ec32f5f..4efa3bfd010bf4ab0b35c82b824c9bb535be17ac 100644
--- a/extensions/common/features/feature.h
+++ b/extensions/common/features/feature.h
@@ -44,6 +44,9 @@ class Feature {
     // will be via the installation of a hosted app, so this may host an
     // extension. This is not affected by the URL matching pattern.
     BLESSED_WEB_PAGE_CONTEXT,
+
+    // A page within webui.
+    WEBUI_CONTEXT,
   };
 
   // The platforms the feature is supported in.