Remove Chrome OS reference in log in common code.

Seeing "Chrome OS Update Engine starting" in Android logcat might be
confusing, changed it to "A/B Update Engine".

Bug: 63666575
Test: mma
Change-Id: Ib1e18cea7b486b84fe6d958c4549bafb56fa2f8d
diff --git a/update_engine_client.cc b/update_engine_client.cc
index 94253de..55206b2 100644
--- a/update_engine_client.cc
+++ b/update_engine_client.cc
@@ -297,7 +297,7 @@
 
   // Boilerplate init commands.
   base::CommandLine::Init(argc_, argv_);
-  brillo::FlagHelper::Init(argc_, argv_, "Chromium OS Update Engine Client");
+  brillo::FlagHelper::Init(argc_, argv_, "A/B Update Engine Client");
 
   // Ensure there are no positional arguments.
   const vector<string> positional_args =