update_engine: Rename "chromeos" -> "brillo" in include paths and namespaces

libchromeos is transitioning to libbrillo and chromeos namespaces
and include directory is changing to brillo.

Bug: 24872993
Change-Id: I770659a95be380a50fe3b2ba9f91d65818f40945
diff --git a/update_manager/real_device_policy_provider.cc b/update_manager/real_device_policy_provider.cc
index f158e27..e7ddb13 100644
--- a/update_manager/real_device_policy_provider.cc
+++ b/update_manager/real_device_policy_provider.cc
@@ -28,7 +28,7 @@
 #include "update_engine/utils.h"
 
 using base::TimeDelta;
-using chromeos::MessageLoop;
+using brillo::MessageLoop;
 using policy::DevicePolicy;
 using std::set;
 using std::string;