Fix mb.py when using isolate archive

This fix is the same as https://crrev.com/c/2105272

Bug: chromium:1062881
Change-Id: Idb24551f4c26100b6983611ca486c0972dca70a6
Reviewers: mbonadei@webrtc.org,  tikuta@chromium.org, dpranke@chromium.org
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/170960
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Ye Kuang <yekuang@google.com>
Cr-Commit-Position: refs/heads/master@{#30826}

tools_webrtc/mb/mb_unittest.py

@@ -760,16 +760,11 @@ class UnitTest(unittest.TestCase):
       '/fake_src/out/Default/base_unittests.runtime_deps': (
           "base_unittests\n"
       ),
+      'out/Default/base_unittests.archive.json': (
+          "{\"base_unittests\":\"fake_hash\"}"),
     }
 
-    def run_stub(cmd, **_kwargs):
-      if os.path.join('tools', 'luci-go', 'isolate') in cmd[0]:
-        return 0, 'fake_hash base_unittests', ''
-      else:
-        return 0, '', ''
-
     mbw = self.fake_mbw(files=files)
-    mbw.Run = run_stub
     self.check(['run', '-s', '-c', 'debug_goma', '//out/Default',
                 'base_unittests'], mbw=mbw, ret=0)
     self.check(['run', '-s', '-c', 'debug_goma', '-d', 'os', 'Win7',