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/evaluation_context.cc b/update_manager/evaluation_context.cc
index 65d9460..0453eac 100644
--- a/update_manager/evaluation_context.cc
+++ b/update_manager/evaluation_context.cc
@@ -32,7 +32,7 @@
 using base::Closure;
 using base::Time;
 using base::TimeDelta;
-using chromeos::MessageLoop;
+using brillo::MessageLoop;
 using chromeos_update_engine::ClockInterface;
 using std::string;
 using std::unique_ptr;