web_dev_style: ignore --css-vars from alphabetical ordering requirement

chrome/browser/web_dev_style/css_checker_test.py

 #!/usr/bin/env python
 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import css_checker
 from os import path as os_path
 import re
 from sys import path as sys_path
 import unittest
@@ skipping 115 matching lines @@
   def testCssAlphaWithLongerDashedProps(self):
     self.VerifyContentsProducesOutput("""
 div {
   border-left: 5px;  /* A hopefully removed comment. */
   border: 5px solid red;
 }""", """
 - Alphabetize properties and list vendor specific (i.e. -webkit) above standard.
     border-left: 5px;
     border: 5px solid red;""")
 
+  def testAlphaIgnoresVariables(self):
+    self.VerifyContentsIsValid("""
+#id {
+  --zzyxx-xylophone: 3px;
+  --aardvark-animal: var(--zzyxz-xylophone);

[dschuyler, 2016/09/15 23:17:36]

maybe add:

--two-line:
    var(--second-line);

--like-a-mixin: {
  foo: 4px;
  bar: 5px;
};

[dschuyler, 2016/09/15 23:48:35]

With my better understanding of the mixins being
removed first, I see that the --like-a-mixin test
is not a good addition.

+}""")
+
   def testCssBracesHaveSpaceBeforeAndNothingAfter(self):
     self.VerifyContentsProducesOutput("""
 /* Hello! */div/* Comment here*/{
   display: block;
 }
 
 blah /* hey! */
 {
   rule: value;
 }
@@ skipping 278 matching lines @@
     opacity: 0.0;
     opacity: 0.;
     border-width: 0mm;
     height: 0cm;
     width: 0in;
 """)
 
 
 if __name__ == '__main__':
   unittest.main()