Partial revert of flag simplification.

Unfortunately it turns out the Android test runner requires
the isolated script flag to be in its current form, or it
doesn't work. This means we have to keep translating the
flag name.

We can get rid of the isolated_script_test_output flag
at least.

Tbr: mbonadei@webrtc.org
Bug: chromium:1051927
Change-Id: I4fdbff980e65332b757b1c95aa6587328411c0ed
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/171809
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30907}

tools_webrtc/mb/mb_unittest.py

@@ -453,9 +453,11 @@ class UnitTest(unittest.TestCase):
     self.assertEqual(files, [
         '../../.vpython',
         '../../testing/test_env.py',
+        '../../tools_webrtc/flags_compatibility.py',
         'base_unittests',
     ])
     self.assertEqual(command, [
+        '../../tools_webrtc/flags_compatibility.py',
         '../../testing/test_env.py',
         './base_unittests',
         '--asan=0',