[bindings] Support is_explicit_nullable for method arguments.

Source/bindings/templates/methods.cpp

 {##############################################################################}
 {% macro generate_method(method, world_suffix) %}
 {% filter conditional(method.conditional_string) %}
 static void {{method.name}}{{method.overload_index}}Method{{world_suffix}}(const v8::FunctionCallbackInfo<v8::Value>& info)
 {
     {# Local variables #}
     {% if method.has_exception_state %}
     ExceptionState exceptionState(ExceptionState::ExecutionContext, "{{method.name}}", "{{interface_name}}", info.Holder(), info.GetIsolate());
     {% endif %}
     {# Overloaded methods have length checked during overload resolution #}
@@ skipping 152 matching lines @@
 {% if not argument.use_permissive_dictionary_conversion %}
 {# Dictionaries must have type Undefined, Null or Object:
 http://heycam.github.io/webidl/#es-dictionary #}
 if (!isUndefinedOrNull(info[{{argument.index}}]) && !info[{{argument.index}}]->IsObject()) {
     {{throw_type_error(method, '"parameter %s (\'%s\') is not an object."' %
                                (argument.index + 1, argument.name)) | indent}}
     return;
 }
 {% endif %}{# not argument.use_permissive_dictionary_conversion #}
 {{argument.v8_value_to_local_cpp_value}};
+{% elif argument.is_explicit_nullable %}
+if (!info[{{argument.index}}]->IsNull()) {
+    {{argument.v8_value_to_local_cpp_value}};

[Jens Widell, 2015/02/24 14:29:03]

This may or may not be the only part that should be conditional. :-) (This macro
is very hard to read; we should probably refactor it.)

I thought about implementing the conditional wrapping in the
generate_arguments() where we already have similar wrapping for handling
optional arguments (with default values), but that's not really a good idea
since it would need to be duplicated then.

Other options are probably available, but I think "refactor this macro" is the
approach we ought to take before thinking much more about this (assuming this
addition turns out to be enough, at least for now.)

[Jens Widell, 2015/02/24 14:30:28]

To clarify: I think this addition here is probably fine.

+}
 {% else %}{# argument.is_nullable #}
 {{argument.v8_value_to_local_cpp_value}};
 {% endif %}{# argument.is_nullable #}
 {# Type checking, possibly throw a TypeError, per:
    http://www.w3.org/TR/WebIDL/#es-type-mapping #}
 {% if argument.has_type_checking_interface and not argument.is_variadic_wrapper_type %}
 {# Type checking for wrapper interface types (if interface not implemented,
    throw a TypeError), per http://www.w3.org/TR/WebIDL/#es-interface
    Note: for variadic arguments, the type checking is done for each matched
    argument instead; see argument.is_variadic_wrapper_type code-path above. #}
@@ skipping 468 matching lines @@
                               if method.overloads else
                               method.runtime_enabled_function) %}
     prototypeObject->Set(v8AtomicString(isolate, "{{method.name}}"), v8::FunctionTemplate::New(isolate, {{cpp_class_or_partial}}V8Internal::{{method.name}}MethodCallback, v8Undefined(), defaultSignature, {{method.number_of_required_arguments}})->GetFunction());
     {% endfilter %}{# runtime_enabled() #}
     {% endfilter %}{# exposed() #}
     {% endfilter %}{# per_context_enabled() #}
     {% endfor %}
     {% endif %}
 }
 {%- endmacro %}