Fix mojom enums check in Feature Policy presubmit

The presubmit check reports an error when the feature policy enum is
modified: "*.json5 and *.mojom are out of sync"

This presubmit error is reported even when the files have identical
enum definitions due to a mistake in the error condition. Instead of
comparing the set of json5_enums with the mojom_source_path, compare
with the set of mojom_enums.

BUG=1105600

Change-Id: Ibc80ac41a37a2102e37edbbdbd6a8a77633051fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2298225Reviewed-by: Charlie Hu <chenleihu@google.com>
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Commit-Queue: Charlie Hu <chenleihu@google.com>
Cr-Commit-Position: refs/heads/master@{#788649}

third_party/blink/public/mojom/feature_policy/PRESUBMIT.py

@@ -131,7 +131,7 @@ def json5_config_checks_factory(mojom_source_path, json5_config_path,
         mojom_messages = "{} are missing in mojom file.\n".format(
             list(mojom_missing_enums)) if mojom_missing_enums else ""
 
-        return [] if json5_enums == mojom_source_path else [
+        return [] if json5_enums == mojom_enums else [
             output_api.PresubmitPromptWarning(
                 "{} and {} are out of sync: {}{}".format(
                     json5_config_path, mojom_source_path, json5_messages,