Fix junit test runner script placement.

testing/android/junit/junit_test.gyp

 # Copyright 2014 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': [
     {
       # GN: //testing/android/junit:junit_test_support
       'target_name': 'junit_test_support',
       'type': 'none',
@@ skipping 16 matching lines @@
       'target_name': 'junit_unit_tests',
       'type': 'none',
       'dependencies': [
         'junit_test_support',
       ],
       'variables': {
         'main_class': 'org.chromium.testing.local.JunitTestMain',
         'src_paths': [
           'javatests/src',
         ],
+        'wrapper_script_name': 'helper/<(_target_name)',
       },
       'includes': [
         '../../../build/host_jar.gypi',
       ],
     },
   ],
 }