bindings: Pass dictionaries to callback methods by const reference

third_party/WebKit/Source/bindings/scripts/v8_callback_interface.py

 # Copyright (C) 2013 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 45 matching lines @@
 def cpp_type(idl_type):
     # FIXME: remove this function by making callback types consistent
     # (always use usual v8_types.cpp_type)
     idl_type_name = idl_type.name
     if idl_type_name == 'String':
         return 'const String&'
     if idl_type_name == 'void':
         return 'void'
     # Callbacks use raw pointers, so raw_type=True
     raw_cpp_type = idl_type.cpp_type_args(raw_type=True)
-    if raw_cpp_type.startswith(('Vector', 'HeapVector', 'WillBeHeapVector')):
+    # Pass containers and dictionaries to callback method by const reference rather than by value
+    if raw_cpp_type.startswith(('Vector', 'HeapVector', 'WillBeHeapVector')) or idl_type.is_dictionary:
         return 'const %s&' % raw_cpp_type
     return raw_cpp_type
 
 IdlTypeBase.callback_cpp_type = property(cpp_type)
 
 
 def callback_interface_context(callback_interface):
     includes.clear()
     includes.update(CALLBACK_INTERFACE_CPP_INCLUDES)
     return {
@@ skipping 45 matching lines @@
         }
 
     argument_declarations = ['ScriptValue thisValue'] if call_with_this_handle else []
     argument_declarations.extend(
         '%s %s' % (argument.idl_type.callback_cpp_type, argument.name)
         for argument in arguments)
     return  {
         'argument_declarations': argument_declarations,
         'arguments': [argument_context(argument) for argument in arguments],
     }