update_engine: Replace scoped_ptr with std::unique_ptr.

BUG=None
TEST=`FEATURES=test emerge-$BOARD update_engine`
TEST=`USE='clang asan' FEATURES=test emerge-$BOARD update_engine`

Change-Id: I55a2f7f53675faaac20ba25f72ed52cf938d7744
Reviewed-on: https://chromium-review.googlesource.com/224189
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
diff --git a/update_manager/default_policy.h b/update_manager/default_policy.h
index 6c1848f..1673609 100644
--- a/update_manager/default_policy.h
+++ b/update_manager/default_policy.h
@@ -5,6 +5,7 @@
 #ifndef UPDATE_ENGINE_UPDATE_MANAGER_DEFAULT_POLICY_H_
 #define UPDATE_ENGINE_UPDATE_MANAGER_DEFAULT_POLICY_H_
 
+#include <memory>
 #include <string>
 
 #include <base/time/time.h>
@@ -74,7 +75,7 @@
   chromeos_update_engine::ClockInterface* clock_;
 
   // An auxiliary state object.
-  scoped_ptr<DefaultPolicyState> aux_state_;
+  std::unique_ptr<DefaultPolicyState> aux_state_;
 
   DISALLOW_COPY_AND_ASSIGN(DefaultPolicy);
 };