[battor agent] Move code for stringifying bytes into a util file

tools/battor_agent/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//testing/test.gni")
 
 # Works only on desktop platforms.
 assert(is_win || is_linux || is_mac)
 
 executable("battor_agent") {
@@ skipping 16 matching lines @@
     "battor_connection.cc",
     "battor_connection.h",
     "battor_connection_impl.cc",
     "battor_connection_impl.h",
     "battor_error.cc",
     "battor_error.h",
     "battor_finder.cc",
     "battor_finder.h",
     "battor_sample_converter.cc",
     "battor_sample_converter.h",
+    "serial_utils.cc",
+    "serial_utils.h",
   ]
   deps = [
     "//base",
     "//device/serial",
     "//net",
   ]
 }
 
 test("battor_agent_unittests") {
   sources = [
     "battor_agent_unittest.cc",
     "battor_connection_impl_unittest.cc",
     "battor_protocol_types_unittest.cc",
     "battor_sample_converter_unittest.cc",
+    "serial_utils_unittest.cc",
   ]
   deps = [
     ":battor_agent_lib",
     "//base",
     "//base/test:run_all_unittests",
     "//base/test:test_support",
     "//device/serial",
     "//device/serial:test_support",
     "//mojo/public/c/system:for_shared_library",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }