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

tools/json_schema_compiler/highlighters/pygments_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 sys
 try:
   import pygments
   from pygments.lexers import CppLexer
   from pygments.formatters import HtmlFormatter
   PYGMENTS_IMPORTED = True
 except ImportError:
   print('It appears that Pygments is not installed. '
     'Can be installed using easy_install Pygments or from http://pygments.org.')
   PYGMENTS_IMPORTED = False
 
 class PygmentsHighlighter(object):
+  def __init__(self):
+    if not PYGMENTS_IMPORTED:
+      raise ImportError('Pygments not installed')
+
   """Highlighter that uses the python pygments library to highlight code.
   """
   def GetCSS(self, style):
-    if PYGMENTS_IMPORTED:
-      formatter = HtmlFormatter(linenos=True,
-          style=pygments.styles.get_style_by_name(style))
-      return formatter.get_style_defs('.highlight')
+    formatter = HtmlFormatter(linenos=True,
+        style=pygments.styles.get_style_by_name(style))
+    return formatter.get_style_defs('.highlight')
 
   def GetCodeElement(self, code, style):
-    if PYGMENTS_IMPORTED:
-      formatter = HtmlFormatter(linenos=True,
-              style=pygments.styles.get_style_by_name(style))
-      return pygments.highlight(code, CppLexer(), formatter)
-    else:
-      return '<pre>Pygments highlighter not installed</pre>'
+    formatter = HtmlFormatter(linenos=True,
+            style=pygments.styles.get_style_by_name(style))
+    return pygments.highlight(code, CppLexer(), formatter)
 
   def DisplayName(self):
     return 'pygments' + ('' if PYGMENTS_IMPORTED else ' (not installed)')
 
   def GetStyles(self):
     return list(pygments.styles.get_all_styles())