[infra] Migrate auto-roller commands to Python3

Another encoding fix and test coverage for it.

No-Try: true
Bug: chromium:1292013
Change-Id: Id54f505848f93b4869710156fa77ad2e258c5dd6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3447905Reviewed-by: Liviu Rau <liviurau@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79007}

tools/release/common_includes.py

@@ -76,6 +76,10 @@ new_path = path_to_depot_tools + os.pathsep + os.environ.get('PATH')
 os.environ['PATH'] = new_path
 
 
+def maybe_decode(obj):
+  return obj.decode('utf-8') if PYTHON3 else obj
+
+
 def TextToFile(text, file_name):
   with open(file_name, "w") as f:
     f.write(text)
@@ -112,7 +116,7 @@ def Command(cmd, args="", prefix="", pipe=True, cwd=None):
   sys.stdout.flush()
   try:
     if pipe:
-      return subprocess.check_output(cmd_line, shell=True, cwd=cwd)
+      return maybe_decode(subprocess.check_output(cmd_line, shell=True, cwd=cwd))
     else:
       return subprocess.check_call(cmd_line, shell=True, cwd=cwd)
   except subprocess.CalledProcessError:

tools/release/test_scripts.py

@@ -29,6 +29,7 @@
 # for py2/py3 compatibility
 from __future__ import print_function
 
+import json
 import os
 import shutil
 import tempfile
@@ -93,6 +94,10 @@ class ToplevelTest(unittest.TestCase):
                 ]
     self.assertEquals(expected, NormalizeVersionTags(input))
 
+  def testCommand(self):
+    """Ensure json can decode the output of commands."""
+    json.dumps(Command('ls', pipe=True))
+
 
 def Cmd(*args, **kwargs):
   """Convenience function returning a shell command test expectation."""