Maintain proper signature_index.

tools/dom/scripts/htmldartgenerator.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
 from generator import AnalyzeOperation, ConstantOutputOrder, \
@@ skipping 245 matching lines @@
           checks.append('(%s is %s || %s == null)' % (
               parameter_name, test_type, parameter_name))
       # There can be multiple presence checks.  We need them all since a later
       # optional argument could have been passed by name, leaving 'holes'.
       checks.extend(['!?%s' % name for name in parameter_names[argument_count:]])
 
       GenerateCall(signature_index, argument_count, checks)
 
     # TODO: Optimize the dispatch to avoid repeated checks.
     if len(signatures) > 1:
-      swapped = False
+      index_swaps = {}
       for signature_index, signature in enumerate(signatures):
         for argument_position, argument in enumerate(signature):
           if argument.type.id != 'ArrayBuffer':
             continue
           candidates = enumerate(
               signatures[signature_index + 1:], signature_index + 1)
           for candidate_index, candidate in candidates:
             if len(candidate) <= argument_position:
               continue
             if candidate[argument_position].type.id != 'ArrayBufferView':
               continue
-            if swapped:
+            if len(index_swaps):
               raise Exception('Cannot deal with more than a single swap')
-            swapped = True
-            signatures = signatures[:]
-            signatures[candidate_index], signatures[signature_index] =\
-                signature, candidate
+            index_swaps[candidate_index] = signature_index
+            index_swaps[signature_index] = candidate_index
 
-      for signature_index, signature in enumerate(signatures):
+      for signature_index in range(len(signatures)):
+        signature_index = index_swaps.get(signature_index, signature_index)
+        signature = signatures[signature_index]
         for argument_position, argument in enumerate(signature):
           if is_optional(signature_index, argument):
             GenerateChecksAndCall(signature_index, argument_position)
         GenerateChecksAndCall(signature_index, len(signature))
       body_emitter.Emit(
           '    throw new ArgumentError("Incorrect number or type of arguments");'
           '\n');
     else:
       signature = signatures[0]
       argument_count = len(signature)
@@ skipping 345 matching lines @@
         walk(interface.parents)
       else:
         walk(interface.parents[1:])
     return result
 
   def _DartType(self, type_name):
     return self._type_registry.DartType(type_name)
 
   def _IsPrivate(self, name):
     return name.startswith('_')