update_engine: Fix build breaks in unit tests on Chrome OS

Some unit tests that compile only on Chrome OS were broken.

Change-Id: I47b27ec49f11137e7549da0b7a8d2d6d9fef768c
diff --git a/omaha_request_action_unittest.cc b/omaha_request_action_unittest.cc
index e5cc7e2..81a7378 100644
--- a/omaha_request_action_unittest.cc
+++ b/omaha_request_action_unittest.cc
@@ -292,6 +292,10 @@
     return "OutputObjectCollectorAction";
   }
   string Type() const { return StaticType(); }
+  using InputObjectType =
+      ActionTraits<OutputObjectCollectorAction>::InputObjectType;
+  using OutputObjectType =
+      ActionTraits<OutputObjectCollectorAction>::OutputObjectType;
   bool has_input_object_;
   OmahaResponse omaha_response_;
 };