Move Dart type narrowing to TypeRegistry.

lib/html/scripts/systemhtml.py

 #!/usr/bin/python
 # Copyright (c) 2012, 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 shared functionality for the system to generate
 Dart:html APIs from the IDL database."""
 
 import emitter
 import os
@@ skipping 1009 matching lines @@
   def CustomJSMembers(self):
     return _js_custom_members
 
   def _HasJavaScriptIndexingBehaviour(self):
     """Returns True if the native object has an indexer and length property."""
     (element_type, requires_indexer) = ListImplementationInfo(
         self._interface, self._database)
     if element_type and requires_indexer: return True
     return False
 
-  def _ShouldNarrowToImplementationType(self, type_name):
-    # TODO(sra): Move into the 'system' and cache the result.
-    do_not_narrow = ['DOMStringList', 'DOMStringMap', 'EventListener',
-                     'IDBAny', 'IDBKey', 'MediaQueryListListener', 'List<Node>',
-                     'NodeList']
-    if type_name in do_not_narrow:
-      return False
-    if self._database.HasInterface(type_name):
-      interface = self._database.GetInterface(type_name)
-      # Callbacks are typedef functions so don't have a class.
-      return 'Callback' not in interface.ext_attrs
-    return False
-
   def _NarrowToImplementationType(self, type_name):
     if type_name == 'Dynamic':
       return type_name
-    if self._ShouldNarrowToImplementationType(type_name):
-      return self._ImplClassName(self._DartType(type_name))
-    return self._DartType(type_name)
+    return self._type_registry.TypeInfo(type_name).narrow_dart_type()
 
   def _NarrowInputType(self, type_name):
     return self._NarrowToImplementationType(type_name)
 
   def _NarrowOutputType(self, type_name):
     return self._NarrowToImplementationType(type_name)
 
   def _FindShadowedAttribute(self, attr, merged_interfaces={}):
     """Returns (attribute, superinterface) or (None, None)."""
     def FindInParent(interface):
@@ skipping 60 matching lines @@
 
     library_emitter = self._multiemitter.FileEmitter(library_file_path)
     library_file_dir = os.path.dirname(library_file_path)
     auxiliary_dir = os.path.relpath(auxiliary_dir, library_file_dir)
     imports_emitter = library_emitter.Emit(
         self._template, AUXILIARY_DIR=massage_path(auxiliary_dir))
     for path in sorted(self._path_to_emitter.keys()):
       relpath = os.path.relpath(path, library_file_dir)
       imports_emitter.Emit(
           "#source('$PATH');\n", PATH=massage_path(relpath))