[code-health] Migrate //third_party/blink/PRESUBMIT.py to python3

Bug: 1212063
Change-Id: Ia96eff3c81b2feab5049caf25a18cd6a71179c96
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2981034
Auto-Submit: Fabrice de Gans <[email protected]>
Commit-Queue: Rick Byers <[email protected]>
Reviewed-by: Rick Byers <[email protected]>
Cr-Commit-Position: refs/heads/master@{#895150}
diff --git a/third_party/blink/PRESUBMIT.py b/third_party/blink/PRESUBMIT.py
index 45f6d63..68013b7 100644
--- a/third_party/blink/PRESUBMIT.py
+++ b/third_party/blink/PRESUBMIT.py
@@ -12,6 +12,8 @@
 import os
 import re
 
+USE_PYTHON3 = True
+
 try:
     # pylint: disable=C0103
     audit_non_blink_usage = imp.load_source(