Fix swarming tests not running in parallel

tools-webrtc/mb/mb_unittest.py

Index: tools-webrtc/mb/mb_unittest.py
diff --git a/tools-webrtc/mb/mb_unittest.py b/tools-webrtc/mb/mb_unittest.py
index 6b1b2ec1c8dead66a9d29fe1a94d8313bee072f6..998133b76702278ea00d0464c0903e719c663ab2 100755
--- a/tools-webrtc/mb/mb_unittest.py
+++ b/tools-webrtc/mb/mb_unittest.py
@@ -441,11 +441,16 @@ class UnitTest(unittest.TestCase):
 
     self.assertEqual(files, [
         '../../testing/test_env.py',
+        '../../third_party/gtest-parallel/gtest-parallel',
+        '../../tools-webrtc/gtest-parallel-wrapper.py',
         'base_unittests',
     ])
     self.assertEqual(command, [
         '../../testing/test_env.py',
+        '../../tools-webrtc/gtest-parallel-wrapper.py',
+        '--output_dir=${ISOLATED_OUTDIR}/test_logs',
         './base_unittests',
+        '--workers=1',
         '--',
         '--asan=0',
         '--msan=0',