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_attempter.h b/update_attempter.h
index a106a2e..7a5e4b7 100644
--- a/update_attempter.h
+++ b/update_attempter.h
@@ -420,8 +420,8 @@
   utils::CpuShares shares_ = utils::kCpuSharesNormal;
 
   // The cpu shares management timeout task id.
-  chromeos::MessageLoop::TaskId manage_shares_id_{
-      chromeos::MessageLoop::kTaskIdNull};
+  brillo::MessageLoop::TaskId manage_shares_id_{
+      brillo::MessageLoop::kTaskIdNull};
 
   // Set to true if an update download is active (and BytesReceived
   // will be called), set to false otherwise.