Once files moved to aos folder and files updated accordingly

Change-Id: Idd26fca1d4dc15407e92859400e1a15a8a142ec3
diff --git a/aos/BUILD b/aos/BUILD
index 5d6831a..89948ab 100644
--- a/aos/BUILD
+++ b/aos/BUILD
@@ -34,3 +34,29 @@
     '//aos/common/logging:binary_log_writer.stripped',
   ],
 )
+
+cc_library(
+  name = 'once',
+  visibility = ['//visibility:public'],
+  hdrs = [
+    'once.h',
+  ],
+  srcs = [
+    'once-tmpl.h',
+  ],
+  deps = [
+    '//aos/common:gtest_prod',
+    '//aos/common:type_traits',
+  ],
+)
+cc_test(
+  name = 'once_test',
+  visibility = ['//visibility:public'],
+  srcs = [
+    'once_test.cc',
+  ],
+  deps = [
+    '//aos/testing:googletest',
+    '//aos:once',
+  ],
+)