web_dev_style: Only run HTMLChecker on .html files

chrome/browser/web_dev_style/html_checker.py

Index: chrome/browser/web_dev_style/html_checker.py
diff --git a/chrome/browser/web_dev_style/html_checker.py b/chrome/browser/web_dev_style/html_checker.py
index 040a4c7103592b76669ceda921a94857da19cf73..2ab90e1fdaa3e8cc82327baf1113041c5337d1d9 100644
--- a/chrome/browser/web_dev_style/html_checker.py
+++ b/chrome/browser/web_dev_style/html_checker.py
@@ -91,6 +91,9 @@ class HtmlChecker(object):
         file_filter=self.file_filter, include_deletes=False)
 
     for f in affected_files:
+      if not f.LocalPath().endswith('.html'):
+        continue
+
       errors = []
 
       for line_number, line in f.ChangedContents():