Add vpython verification presubmit

R=machenbach@chromium.org

Bug: chromium:777893
Change-Id: I2816934494309da458589b7d9b0c46fba9beaf38
Reviewed-on: https://chromium-review.googlesource.com/741221
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49102}

PRESUBMIT.py

@@ -281,6 +281,8 @@ def _CommonChecks(input_api, output_api):
   results.extend(_CheckMissingFiles(input_api, output_api))
   results.extend(_CheckJSONFiles(input_api, output_api))
   results.extend(_CheckMacroUndefs(input_api, output_api))
+  results.extend(input_api.RunTests(
+    input_api.canned_checks.CheckVPythonSpec(input_api, output_api)))
   return results