Python3Migration-PresubmitChecks: weblayer/browser

This CL is part of a larger effort to deprecate python2 in PRESUBMIT.
json_schema_compiler's PRESUBMIT file will now run unit tests in
python3.

Bug: 1212129
Change-Id: I911900f04e4deb830f6b4ef772d873c866292c96
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2927729
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Scott Violet <sky@chromium.org>
Auto-Submit: Ari Chivukula <arichiv@chromium.org>
Commit-Queue: Ari Chivukula <arichiv@chromium.org>
Cr-Commit-Position: refs/heads/master@{#888245}

weblayer/browser/java/org/chromium/weblayer_private/interfaces/PRESUBMIT.py

@@ -15,6 +15,8 @@
 import sys
 import tempfile
 
+USE_PYTHON3 = True
+
 _INCOMPATIBLE_API_ERROR_STRING = """You have made an incompatible API change.
 Generally this means one of the following:
   A function has been removed.