Adding support for user interface extensions.

Change-Id: I1e41d16efc11be31ad4c2fb0c09e86e3dfd26706
diff --git a/core/api/src/test/resources/css.html b/core/api/src/test/resources/css.html
new file mode 100644
index 0000000..3079957
--- /dev/null
+++ b/core/api/src/test/resources/css.html
@@ -0,0 +1,2 @@
+foo-css
+bar-css
\ No newline at end of file