Explicitly implementing some DOM iterable APIs for performance

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 monitored
@@ skipping 694 matching lines @@
     # and
     #
     #   class YImpl extends ListBase<T> { copies of transitive XImpl methods; }
     #
 
     ext_attrs = self._interface.ext_attrs
     has_indexed_getter = ('IndexedGetter' in ext_attrs or
       'CustomIndexedSetter' in ext_attrs)
 
     if has_indexed_getter:
+      indexed_getter = ('JS("%s", "#[#]", this, index)' %
+          self.SecureOutputType(element_type));
+    elif any(op.id == 'getItem' for op in self._interface.operations):
+      indexed_getter = 'this.getItem(index)'
+    elif any(op.id == 'item' for op in self._interface.operations):
+      indexed_getter = 'this.item(index)'
+
+    if indexed_getter:
       self._members_emitter.Emit(
           '\n'
-          '  $TYPE operator[](int index) => '
-          'JS("$TYPE", "#[#]", this, index);\n',
-          TYPE=self.SecureOutputType(element_type))
-    else:
-      if any(op.id == 'getItem' for op in self._interface.operations):
-        indexed_getter = 'this.getItem(index)'
-      elif any(op.id == 'item' for op in self._interface.operations):
-        indexed_getter = 'this.item(index)'
-      self._members_emitter.Emit(
-          '\n'
-          '  $TYPE operator[](int index) => $INDEXED_GETTER;\n',
+          '  $TYPE operator[](int index) {\n'
+          '    if (JS("bool", "# >>> 0 !== # || # >= #", index,\n'
+          '        index, index, length))\n'
+          '      throw new RangeError.range(index, 0, length);\n'
+          '    return $INDEXED_GETTER;\n'
+          '  }',
           INDEXED_GETTER=indexed_getter,
           TYPE=self.SecureOutputType(element_type))
 
     if 'CustomIndexedSetter' in self._interface.ext_attrs:
       self._members_emitter.Emit(
           '\n'
           '  void operator[]=(int index, $TYPE value) {'
           ' JS("void", "#[#] = #", this, index, value); }',
           TYPE=self._NarrowInputType(element_type))
     else:
@@ skipping 430 matching lines @@
     for library_name in libraries:
       self._libraries[library_name] = DartLibrary(
           library_name, template_loader, library_type, output_dir)
 
   def AddFile(self, basename, library_name, path):
     self._libraries[library_name].AddFile(path)
 
   def Emit(self, emitter, auxiliary_dir):
     for lib in self._libraries.values():
       lib.Emit(emitter, auxiliary_dir)