Fix syntax highlighting in JSON Schema Compiler's preview server: don't crash

tools/json_schema_compiler/highlighters/none_highlighter.py

 # Copyright (c) 2012 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 cgi
+
 class NoneHighlighter(object):
   """Highlighter that just wraps code in a <pre>.
   """
   def GetCSS(self, style):
     return ''
 
   def GetCodeElement(self, code, style):
-    return '<pre>' + code + '</pre>'
+    return '<pre>' + cgi.escape(code) + '</pre>'
 
   def DisplayName(self):
     return 'none'
 
   def GetStyles(self):
     return []