Add supported checks to the SVG library, and library cleanup.

tools/dom/scripts/monitored.py

 #!/usr/bin/python
 # Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 """This module provides maps and sets that report unused elements."""
 
 _monitored_values = []
 
 
@@ skipping 11 matching lines @@
   """Wrapper for a read-only dict that reports unused keys."""
 
   def __init__(self, name, map):
     super(Dict, self).__init__(name)
     self._map = map
 
   def __getitem__(self, key):
     self._used_keys.add(key)
     return self._map[key]
 
+  def __setitem__(self, key, value):
+    self._map[key] = value
+
   def __contains__(self, key):
     self._used_keys.add(key)
     return key in self._map
 
   def __iter__(self):
     return self._map.__iter__()
 
   def get(self, key, default=None):
     self._used_keys.add(key)
     return self._map.get(key, default)
@@ skipping 12 matching lines @@
     self._set = a_set
 
   def __contains__(self, key):
     self._used_keys.add(key)
     return key in self._set
 
   def CheckUsage(self):
     for v in sorted(self._set):
       if v not in self._used_keys:
         print "set '%s' has unused key '%s'" % (self.name, v)