Convert mojo_public_system_unittests to run exclusively on Swarming

third_party/mojo/mojo_edk_tests.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.
 
 {
   'includes': [
     'mojo_variables.gypi',
   ],
   'targets': [
     {
@@ skipping 283 matching lines @@
           'dependencies': [
             'mojo_public_environment_unittests',
           ],
           'includes': [
             '../../build/isolate.gypi',
           ],
           'sources': [
             'mojo_public_environment_unittests.isolate',
           ],
         },
+        {
+          'target_name': 'mojo_public_system_unittests_run',
+          'type': 'none',
+          'dependencies': [
+            'mojo_public_system_unittests',
+          ],
+          'includes': [
+            '../../build/isolate.gypi',
+          ],
+          'sources': [
+            'mojo_public_system_unittests.isolate',
+          ],
+        },
       ],
     }],
   ],
 }