Make nullable members of IDL dictionaries contain null in JS when unset

third_party/WebKit/Source/bindings/templates/dictionary_v8.cpp

 {% from 'utilities.cpp' import declare_enum_validation_variable %}
 {% include 'copyright_block.txt' %}
 #include "{{v8_original_class}}.h"
 
 {% for filename in cpp_includes if filename != '%s.h' % v8_class %}
 #include "{{filename}}"
 {% endfor %}
 
 namespace blink {
 
@@ skipping 99 matching lines @@
     if (impl.{{member.has_method_name}}()) {
         {% if member.is_object %}
         ASSERT(impl.{{member.cpp_name}}().isObject());
         {% endif %}
         if (!v8CallBoolean(dictionary->CreateDataProperty(isolate->GetCurrentContext(), v8String(isolate, "{{member.name}}"), {{member.cpp_value_to_v8_value}})))
             return false;
     {% if member.v8_default_value %}
     } else {
         if (!v8CallBoolean(dictionary->CreateDataProperty(isolate->GetCurrentContext(), v8String(isolate, "{{member.name}}"), {{member.v8_default_value}})))
             return false;
+    {% elif member.is_nullable %}
+    } else {
+        if (!v8CallBoolean(dictionary->CreateDataProperty(isolate->GetCurrentContext(), v8String(isolate, "{{member.name}}"), v8::Null(isolate))))
+            return false;
     {% elif member.is_required %}
     } else {
         ASSERT_NOT_REACHED();
     {% endif %}
     }
 
     {% endfor %}
     return true;
 }
 
 {{cpp_class}} NativeValueTraits<{{cpp_class}}>::nativeValue(v8::Isolate* isolate, v8::Local<v8::Value> value, ExceptionState& exceptionState)
 {
     {{cpp_class}} impl;
     {{v8_class}}::toImpl(isolate, value, impl, exceptionState);
     return impl;
 }
 
 } // namespace blink