Remive uses of "void operator[]() => ..." in the html library and enable return type checks for all…

sdk/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 464 matching lines @@
     #   class YImpl extends ListBase<T> { copies of transitive XImpl methods; }
     #
     self._members_emitter.Emit(
         '\n'
         '  $TYPE operator[](int index) => JS("$TYPE", "#[#]", this, index);\n',
         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);\n',
+          '  void operator[]=(int index, $TYPE value) {'
+          ' JS("void", "#[#] = #", this, index, value); }',
           TYPE=self._NarrowInputType(element_type))
     else:
       self._members_emitter.Emit(
           '\n'
           '  void operator[]=(int index, $TYPE value) {\n'
           '    throw new UnsupportedError("Cannot assign element of immutable List.");\n'
           '  }\n',
           TYPE=self._NarrowInputType(element_type))
 
     # TODO(sra): Use separate mixins for mutable implementations of List<T>.
@@ skipping 472 matching lines @@
       'svg': DartLibrary('svg', template_loader, library_type, output_dir),
       'html': DartLibrary('html', 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)