DevTools: consistently use Maybe for optional values in the protocol generator.

third_party/WebKit/Source/platform/inspector_protocol/Frontend_cpp.template

 // This file is generated
 
 // Copyright (c) 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "platform/inspector_protocol/{{class_name}}.h"
 
 #include "wtf/text/CString.h"
 #include "wtf/text/WTFString.h"
 
 namespace blink {
 namespace protocol {
 
 Frontend::Frontend(FrontendChannel* frontendChannel)
     : m_frontendChannel(frontendChannel)
 {% for domain in api.domains %}
     , m_{{domain.domain | lower}}(frontendChannel)
 {% endfor %}
 {
 }
 
 {% for domain in api.domains %}
   {% for event in domain.events %}
     {% if "handlers" in event and not ("renderer" in event["handlers"]) %}{% continue %}{% endif %}
 void Frontend::{{domain.domain}}::{{event.name}}(
     {%- for parameter in event.parameters %}
       {% if "optional" in parameter -%}
-        {{resolve_type(parameter).optional_pass_type}}
+        const Maybe<{{resolve_type(parameter).raw_type}}>&
       {%- else -%}
         {{resolve_type(parameter).pass_type}}
       {%- endif %} {{parameter.name}}{%- if not loop.last -%}, {% endif -%}
     {% endfor -%})
 {
     RefPtr<JSONObject> jsonMessage = JSONObject::create();
     jsonMessage->setString("method", "{{domain.domain}}.{{event.name}}");
     RefPtr<JSONObject> paramsObject = JSONObject::create();
     {% for parameter in event.parameters %}
       {% if "optional" in parameter %}
-    {{resolve_type(parameter).optional_type}} opt_{{parameter.name}} = {{parameter.name}};
-    if (hasValue(opt_{{parameter.name}}))
-        paramsObject->setValue("{{parameter.name}}", toValue({{resolve_type(parameter).from_optional_out % ("opt_" + parameter.name)}}));
+    if ({{parameter.name}}.isJust())
+        paramsObject->setValue("{{parameter.name}}", toValue({{parameter.name}}));
       {% else %}
     paramsObject->setValue("{{parameter.name}}", toValue({{parameter.name}}));
       {% endif %}
     {% endfor %}
     jsonMessage->setObject("params", paramsObject);
     if (m_frontendChannel)
         m_frontendChannel->sendProtocolNotification(jsonMessage.release());
 }
   {% endfor %}
 {% endfor %}
 
 } // namespace protocol
 } // namespace blink