[testrunner] prevent from presubmit masking testrunner end-to-end tests

R=machenbach@chromium.org
CC=​​yangguo@chromium.org,sergiyb@chromium.org

No-Try: true
Bug: v8:8174,v8:8728,v8:8763
Change-Id: I27faa43e775b4a834a7c2af3ec1407afb71bb06e
Reviewed-on: https://chromium-review.googlesource.com/c/1447714
Commit-Queue: Tamer Tas <tmrts@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59231}

tools/testrunner/PRESUBMIT.py

@@ -5,6 +5,6 @@
 def CheckChangeOnCommit(input_api, output_api):
   tests = input_api.canned_checks.GetUnitTestsInDirectory(
       input_api, output_api, '../unittests', whitelist=['run_tests_test.py$'])
-  tests = input_api.canned_checks.GetUnitTestsInDirectory(
+  tests += input_api.canned_checks.GetUnitTestsInDirectory(
     input_api, output_api, 'testproc', whitelist=['variant_unittest.py$'])
   return input_api.RunTests(tests)