Restore sample app target

Summary:
Restore the open source sample target to restore the Travis build.

I'm not sure the python code can parse this data yet, so I'm not gonna flip the
target over to have processmetadata as well.

Differential Revision: D6717041

fbshipit-source-id: 516054861117f7000cd9bbd9c9ab03055515e5dc

java/main/com/facebook/loom/sample/BUCK

@@ -82,6 +82,14 @@ def loom_sample_app(providers):
 
 loom_sample_app(None)
 
+# Referred to by open source buckconfig, don't forget to update it there.
+loom_sample_app([
+    "atrace",
+    "stacktrace",
+    "systemcounters",
+    "threadmetadata",
+])
+
 loom_sample_app([
     "atrace",
     "stacktrace",