GitLab

Do not call check-webkit-style with empty affected file list as it tries to check all edited files including the skipped ones

This patch changes _CheckStyle to prevent calling check-webkit-style with empty arguments list if all files got filtered out.

BUG=635619
TEST=third_party/WebKit/PRESUBMIT_test.py

Review-Url: https://codereview.chromium.org/2236993002
Cr-Commit-Position: refs/heads/master@{#414472}