presubmit: use dict.values in python3

python3 does not support dict.itervalues. python2 will still work
with dict.values in case the file is changed back to python2.

//PRESUBMIT.py was ported to python3 here:
https://crrev.com/c/2877897

BUG=816629
TEST=run git cl presubmit without python errors

Change-Id: I09d8d92e60f0fab67eca7446c91c5244aec165de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2895848
Reviewed-by: Dirk Pranke <[email protected]>
Commit-Queue: Dirk Pranke <[email protected]>
Cr-Commit-Position: refs/heads/master@{#883156}
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index cca55f5e..032995cb 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -2910,7 +2910,7 @@
     try:
       with open(owners_file) as f:
         lines = set(f.read().splitlines())
-        for entry in patterns.itervalues():
+        for entry in patterns.values():
           entry['rules'] = [rule for rule in entry['rules'] if rule not in lines
                            ]
     except IOError: