Add toDouble() helper, and use toFloat()/toDouble() for conversions

Source/bindings/scripts/v8_interface.py

 # Copyright (C) 2013 Google Inc. All rights reserved.
 # coding=utf-8
 #
 # 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
@@ skipping 1007 matching lines @@
 def property_setter(setter):
     idl_type = setter.arguments[1].idl_type
     extended_attributes = setter.extended_attributes
     is_raises_exception = 'RaisesException' in extended_attributes
     return {
         'has_type_checking_interface':
             has_extended_attribute_value(setter, 'TypeChecking', 'Interface') and
             idl_type.is_wrapper_type,
         'idl_type': idl_type.base_type,
         'is_custom': 'Custom' in extended_attributes,
-        'has_exception_state': is_raises_exception or
-                               idl_type.is_integer_type,
+        'has_exception_state': (is_raises_exception or
+                                idl_type.v8_conversion_needs_exception_state),
         'is_raises_exception': is_raises_exception,
         'name': cpp_name(setter),
         'v8_value_to_local_cpp_value': idl_type.v8_value_to_local_cpp_value(
             extended_attributes, 'v8Value', 'propertyValue'),
     }
 
 
 def property_deleter(deleter):
     idl_type = deleter.idl_type
     if str(idl_type) != 'boolean':
@@ skipping 106 matching lines @@
         deleter = next(
             method
             for method in interface.operations
             if ('deleter' in method.specials and
                 len(method.arguments) == 1 and
                 str(method.arguments[0].idl_type) == 'DOMString'))
     except StopIteration:
         return None
 
     return property_deleter(deleter)