Add an explicit dependency on device_serial_mojo to battor agent.

tools/battor_agent/battor_agent.gyp

 # 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.
 
 {
   'targets': [
     {
       'target_name': 'battor_agent',
       'type': 'executable',
       'include_dirs': [
         '../..',
       ],
       'dependencies': [
         'battor_agent_lib',
         '../../device/serial/serial.gyp:device_serial',
+        '../../device/serial/serial.gyp:device_serial_mojo',
         '../../third_party/mojo/mojo_public.gyp:mojo_environment_standalone',
         '../../third_party/mojo/mojo_public.gyp:mojo_public',
       ],
       'sources': [
         'battor_agent_bin.cc',
       ],
     },
     {
       'target_name': 'battor_agent_lib',
       'type': 'static_library',
       'include_dirs': [
         '../..',
       ],
       'sources': [
         'battor_agent.cc',
         'battor_agent.h',
         'battor_error.h',
       ],
       'dependencies': [
         '../../base/base.gyp:base',
         '../../device/serial/serial.gyp:device_serial',
+        '../../device/serial/serial.gyp:device_serial_mojo',
       ]
     },
   ],
 }