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

tools/json_schema_compiler/previewserver.py

 #!/usr/bin/env python
 
 # 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.
 """Server for viewing the compiled C++ code from tools/json_schema_compiler.
 """
 
 import cc_generator
 import code
@@ skipping 303 matching lines @@
       help='port to run the server on')
 
   (opts, argv) = parser.parse_args()
 
   try:
     print('Starting previewserver on port %d' % opts.port)
     print('The extension documentation can be found at:')
     print('')
     print('  http://localhost:%d/chrome/common/extensions/api' % opts.port)
     print('')
-    server = PreviewHTTPServer(('', int(opts.port)), CompilerHandler,
-      {
-        'pygments': pygments_highlighter.PygmentsHighlighter(),
-        'hilite': hilite_me_highlighter.HiliteMeHighlighter(),
-        'none': none_highlighter.NoneHighlighter(),
-      })
+
+    highlighters = {
+      'hilite': hilite_me_highlighter.HiliteMeHighlighter(),
+      'none': none_highlighter.NoneHighlighter()
+    }
+    try:
+      highlighters['pygments'] = pygments_highlighter.PygmentsHighlighter()
+    except ImportError as e:
+      pass
+
+    server = PreviewHTTPServer(('', int(opts.port)),
+                               CompilerHandler,
+                               highlighters)
     server.serve_forever()
   except KeyboardInterrupt:
     server.socket.close()