Add presubmit check to warn about <label> for usage.

chrome/browser/PRESUBMIT.py

Index: chrome/browser/PRESUBMIT.py
diff --git a/chrome/browser/PRESUBMIT.py b/chrome/browser/PRESUBMIT.py
index 14d72c70e708d4ae14c6b60f2b798dae55a612f6..eca561c9178f0b23d2919c1e3b76018c5681e674 100644
--- a/chrome/browser/PRESUBMIT.py
+++ b/chrome/browser/PRESUBMIT.py
@@ -35,6 +35,7 @@ def _CommonChecks(input_api, output_api):
       path.join(cwd, 'PRESUBMIT.py'),
       path.join(cwd, 'test_presubmit.py'),
       path.join(cwd, 'web_dev_style', 'css_checker.py'),
+      path.join(cwd, 'web_dev_style', 'html_checker.py'),
       path.join(cwd, 'web_dev_style', 'js_checker.py'),
   )
   if any(f for f in affected_files if f in would_affect_tests):
@@ -47,7 +48,8 @@ def _CommonChecks(input_api, output_api):
 
   try:
     sys.path = [cwd] + old_path
-    from web_dev_style import resource_checker, css_checker, js_checker
+    from web_dev_style import (resource_checker, css_checker, html_checker,
+                               js_checker)
 
     search_dirs = (resources, webui)
     def _html_css_js_resource(p):
@@ -63,6 +65,8 @@ def _CommonChecks(input_api, output_api):
         input_api, output_api, file_filter=is_resource).RunChecks())
     results.extend(css_checker.CSSChecker(
         input_api, output_api, file_filter=is_resource).RunChecks())
+    results.extend(html_checker.HtmlChecker(
+        input_api, output_api, file_filter=is_resource).RunChecks())
     results.extend(js_checker.JSChecker(
         input_api, output_api, file_filter=is_resource).RunChecks())
   finally: