js_checker.py: Restore smoke tests for linting violations.

tools/web_dev_style/js_checker.py

Index: tools/web_dev_style/js_checker.py
diff --git a/tools/web_dev_style/js_checker.py b/tools/web_dev_style/js_checker.py
index 7d48c3f853bacc7a347a74a378355139f50f4133..5e202be2d93f3014ed0777b8b62c1debf5c48a79 100644
--- a/tools/web_dev_style/js_checker.py
+++ b/tools/web_dev_style/js_checker.py
@@ -62,14 +62,13 @@ class JSChecker(object):
     return self.RegexCheck(i, line, r"(?<!this)(\.\$)[\[\.]",
         "Please only use this.$.localId, not element.$.localId")
 
-  def RunEsLintChecks(self, affected_js_files):
+  def RunEsLintChecks(self, affected_js_files_paths, format='stylish'):
     """Runs lint checks using ESLint. The ESLint rules being applied are defined
        in the .eslintrc.js configuration file.
     """
-    os_path = self.input_api.os_path
-
     try:
       # Import ESLint.
+      os_path = self.input_api.os_path
       _HERE_PATH = os_path.dirname(os_path.realpath(__file__))
       _SRC_PATH = os_path.normpath(os_path.join(_HERE_PATH, '..', '..'))
       import sys
@@ -79,16 +78,10 @@ class JSChecker(object):
     finally:
       sys.path = old_sys_path
 
-    # Extract paths to be passed to ESLint.
-    affected_js_files_paths = []
-    presubmit_path = self.input_api.PresubmitLocalPath()
-    for f in affected_js_files:
-      affected_js_files_paths.append(
-          os_path.relpath(f.AbsoluteLocalPath(), presubmit_path))
-
     output = node.RunNode([
         node_modules.PathToEsLint(),
         '--color',
+        '--format', format,
         '--ignore-pattern \'!.eslintrc.js\'',
         ' '.join(affected_js_files_paths)])
 
@@ -124,8 +117,14 @@ class JSChecker(object):
     affected_js_files = filter(lambda f: f.LocalPath().endswith('.js'),
                                affected_files)
 
+    # Extract paths to be passed to ESLint.
+    def get_path(f):
+      return self.input_api.os_path.relpath(
+          f.AbsoluteLocalPath(), self.input_api.PresubmitLocalPath())
+
     if affected_js_files:
-      results += self.RunEsLintChecks(affected_js_files)
+      affected_js_files_paths = map(get_path, affected_js_files)
+      results += self.RunEsLintChecks(affected_js_files_paths)
 
     for f in affected_js_files:
       error_lines = []