Use Chromium's mirror of github for gtest-parallel.

- Move gtest-parallel-wrapper.py to tools-webrtc.
- Update mb.py and mb_unittest.py

BUG=webrtc:7391
NOTRY=True
R=kjellander@webrtc.org

Review-Url: https://codereview.webrtc.org/2785653002
Cr-Commit-Position: refs/heads/master@{#17453}
diff --git a/tools-webrtc/mb/mb.py b/tools-webrtc/mb/mb.py
index 5e9f388..52c3987 100755
--- a/tools-webrtc/mb/mb.py
+++ b/tools-webrtc/mb/mb.py
@@ -1092,12 +1092,12 @@
       if gtest_parallel:
         extra_files += [
             '../../third_party/gtest-parallel/gtest-parallel',
-            '../../third_party/gtest-parallel/gtest-parallel-wrapper.py',
+            '../../tools-webrtc/gtest-parallel-wrapper.py',
         ]
         sep = '\\' if self.platform == 'win32' else '/'
         output_dir = '${ISOLATED_OUTDIR}' + sep + 'test_logs'
         gtest_parallel_wrapper = [
-            '../../third_party/gtest-parallel/gtest-parallel-wrapper.py',
+            '../../tools-webrtc/gtest-parallel-wrapper.py',
             '--output_dir=%s' % output_dir,
         ]