Fix GetPylint with USE_PYTHON3=True

kwargs['stdin'] is passed in to subprocess communicate(), which
expects bytes, not str.

Bug: 1215602
Change-Id: I95326eed08cffecd31abc6b0380de2a3c2ff3dd6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2929386
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Dan H <harringtond@chromium.org>

presubmit_canned_checks.py

@@ -944,6 +944,7 @@ def GetPylint(input_api,
   input_api.logging.debug('  with extra PYTHONPATH: %r', extra_paths_list)
 
   def GetPylintCmd(flist, extra, parallel):
+    import sys
     # Windows needs help running python files so we explicitly specify
     # the interpreter to use. It also has limitations on the size of
     # the command-line, so we pass arguments via a pipe.
@@ -975,6 +976,8 @@ def GetPylint(input_api,
       description += ' on %d cores' % input_api.cpu_count
 
     kwargs['stdin'] = '\n'.join(args + flist)
+    if sys.version_info.major != 2:
+      kwargs['stdin'] = kwargs['stdin'].encode('utf-8')
 
     return input_api.Command(
         name='Pylint (%s)' % description,