Add a hashCode that delegates to JS for everything that defines ==

tools/dom/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 logging
@@ skipping 571 matching lines @@
       else:
         class_modifiers = 'abstract '
 
     native_spec = ''
     if not IsPureInterface(self._interface.id):
       native_spec = self._backend.NativeSpec()
 
     class_name = self._interface_type_info.implementation_name()
 
     js_interop_equivalence_op = \
-      '  bool operator ==(other) => unwrap_jso(other) == unwrap_jso(this) || identical(this, other);\n'
+      '  bool operator ==(other) => unwrap_jso(other) == unwrap_jso(this) || identical(this, other);\n' \
+      + '  int get hashCode => unwrap_jso(this).hashCode;\n'
     # ClientRect overrides the equivalence operator.
     if interface_name == 'ClientRect' or interface_name == 'DomRectReadOnly':
         js_interop_equivalence_op = ''
 
     js_interop_wrapper = '''
 
   static {0} internalCreate{0}() {{
     return new {0}._internalWrap();
   }}
 
@@ skipping 767 matching lines @@
 
   def AddFile(self, basename, library_name, path):
     self._libraries[library_name].AddFile(path)
 
   def AddTypeEntry(self, library_name, idl_name, dart_name):
     self._libraries[library_name].AddTypeEntry(idl_name, dart_name)
 
   def Emit(self, emitter, auxiliary_dir):
     for lib in self._libraries.values():
       lib.Emit(emitter, auxiliary_dir)