[Test Automation] Use xvfb directly instead of xvfb-run

Thereby fix signal handling for SIGTERM and SIGINT.

The steps needed to start Xvfb are drawn from:
https://github.com/cgoldberg/xvfbwrapper/blob/master/xvfbwrapper.py
https://github.com/revnode/xvfb-run/blob/master/xvfb-run

Added unit tests to presubmit to test xvfb.py


Bug: 932240
Change-Id: I3b9439991697ae94e98b93e4f1fcfd411a451536
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1548424
Commit-Queue: Ilia Samsonov <[email protected]>
Reviewed-by: Caleb Rouleau <[email protected]>
Reviewed-by: Marc-Antoine Ruel <[email protected]>
Reviewed-by: Dirk Pranke <[email protected]>
Reviewed-by: John Chen <[email protected]>
Cr-Commit-Position: refs/heads/master@{#652562}
diff --git a/testing/PRESUBMIT.py b/testing/PRESUBMIT.py
index 5e8fc90..8a8f0d7 100644
--- a/testing/PRESUBMIT.py
+++ b/testing/PRESUBMIT.py
@@ -12,6 +12,8 @@
 def CommonChecks(input_api, output_api):
   output = []
   blacklist = [r'gmock.*', r'gtest.*']
+  output.extend(input_api.canned_checks.RunUnitTestsInDirectory(
+      input_api, output_api, '.', [r'^.+_unittest\.py$']))
   output.extend(input_api.canned_checks.RunPylint(
       input_api, output_api, black_list=blacklist))
   return output