Generate contains() method for list mixin only if not already defined.

lib/html/scripts/systemnative.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 systems to generate
 native binding from the IDL database."""
 
 import emitter
 import os
@@ skipping 380 matching lines @@
             '  }\n',
             TYPE=dart_element_type)
 
     # The list interface for this class is manually generated.
     if self._interface.id == 'NodeList':
       return
 
     # TODO(sra): Use separate mixins for mutable implementations of List<T>.
     # TODO(sra): Use separate mixins for typed array implementations of List<T>.
     template_file = 'immutable_list_mixin.darttemplate'
-    template = self._template_loader.Load(template_file)
+    has_contains = any(op.id == 'contains' for op in self._interface.operations)
+    template = self._template_loader.Load(
+        template_file,
+        {'DEFINE_CONTAINS': not has_contains})
     self._members_emitter.Emit(template, E=dart_element_type)
 
   def AmendIndexer(self, element_type):
     # If interface is marked as having native indexed
     # getter or setter, we must emit overrides as it's not
     # guaranteed that the corresponding methods in C++ would be
     # virtual.  For example, as of time of writing, even though
     # Uint8ClampedArray inherits from Uint8Array, ::set method
     # is not virtual and accessing it through Uint8Array pointer
     # would lead to wrong semantics (modulo vs. clamping.)
@@ skipping 449 matching lines @@
   def EmitResolver(self, template, output_dir):
     file_path = os.path.join(output_dir, 'DartResolver.cpp')
     includes_emitter, body_emitter = self._emitters.FileEmitter(file_path).Emit(template)
     for header_file in self._headers_list:
       path = os.path.relpath(header_file, output_dir)
       includes_emitter.Emit('#include "$PATH"\n', PATH=path)
       body_emitter.Emit(
           '    if (Dart_NativeFunction func = $CLASS_NAME::resolver(name, argumentCount))\n'
           '        return func;\n',
           CLASS_NAME=os.path.splitext(os.path.basename(path))[0])