[bindings] Eliminate custom bindings for DeviceOrientationEvent.

Source/bindings/templates/conversions.cpp

 {% macro v8_value_to_local_cpp_value(thing) %}
 {# This indirection is just to avoid spurious white-space lines. #}
 {{generate_v8_value_to_local_cpp_value(thing) | trim}}
 {%- endmacro %}
 
 
 {% macro generate_v8_value_to_local_cpp_value(thing) %}
 {% set item = thing.v8_value_to_local_cpp_value or thing %}
 {% if item.error_message %}
 /* {{item.error_message}} */
 {% else %}
 {% if item.declare_variable %}
 {% if item.assign_expression %}
 {{item.cpp_type}} {{item.cpp_name}} = {{item.assign_expression}};
 {% else %}
 {{item.cpp_type}} {{item.cpp_name}};
 {% endif %}
 {% else %}{# item.declare_variable #}
 {% if item.assign_expression %}
+{% if thing.is_undefined_to_null %}
+{{item.cpp_name}}Value = {{item.assign_expression}};
+{{item.cpp_name}} = &{{item.cpp_name}}Value;
+{% else %}
 {{item.cpp_name}} = {{item.assign_expression}};
 {% endif %}
+{% endif %}
 {% endif %}{# item.declare_variable #}
 {% if item.set_expression %}
 {{item.set_expression}};
 {% endif %}
 {% if item.check_expression %}
 if ({{item.check_expression}})
     return{% if item.return_expression %} {{item.return_expression}}{% endif %};
 {% endif %}{# item.check_expression #}
 {% endif %}{# item.error_message #}
 {% endmacro %}
 
 
 {% macro declare_enum_validation_variable(enum_values) %}
 static const char* validValues[] = {
 {% for enum_value in enum_values %}
     "{{enum_value}}",
 {% endfor %}
 };
 {%-endmacro %}