[py3] Migrate tools/binary_size PRESUBMIT

Bug: 1212092
Change-Id: I0c16d1a0a64924eaee869ac08f64f4ff6d9baa14
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2946145
Auto-Submit: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Cr-Commit-Position: refs/heads/master@{#892267}

tools/binary_size/PRESUBMIT.py

@@ -8,6 +8,9 @@
 for more details about the presubmit API built into depot_tools.
 """
 
+USE_PYTHON3 = True
+
+
 def CommonChecks(input_api, output_api):
   output = []
   output.extend(input_api.canned_checks.RunPylint(input_api, output_api))