[swarming] Run unittests together with default tests.

test/default.gyp

 # Copyright 2015 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'conditions': [
     ['test_isolation_mode != "noop"', {
       'targets': [
         {
           'target_name': 'default_run',
           'type': 'none',
           'dependencies': [
             'cctest/cctest.gyp:cctest_run',
             'intl/intl.gyp:intl_run',
             'message/message.gyp:message_run',
             'mjsunit/mjsunit.gyp:mjsunit_run',
             'preparser/preparser.gyp:preparser_run',
+            'unittests/unittests.gyp:unittests_run',
           ],
           'includes': [
             '../build/features.gypi',
             '../build/isolate.gypi',
           ],
           'sources': [
             'default.isolate',
           ],
         },
       ],
     }],
   ],
 }