Mojo C++ bindings: support mapping mojo string to WTF::String.

mojo/public/tools/bindings/generators/cpp_templates/module.cc.tmpl

 // Copyright 2013 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.
 
 {%- if variant -%}
 {%-   set variant_path = "%s-%s"|format(module.path, variant) -%}
 {%- else -%}
 {%-   set variant_path = module.path -%}
 {%- endif %}
 
@@ skipping 18 matching lines @@
 #include "mojo/public/cpp/bindings/lib/bindings_serialization.h"
 #include "mojo/public/cpp/bindings/lib/bounds_checker.h"
 #include "mojo/public/cpp/bindings/lib/map_data_internal.h"
 #include "mojo/public/cpp/bindings/lib/message_builder.h"
 #include "mojo/public/cpp/bindings/lib/validate_params.h"
 #include "mojo/public/cpp/bindings/lib/validation_errors.h"
 #include "mojo/public/cpp/bindings/lib/validation_util.h"
 #include "mojo/public/cpp/environment/lib/scoped_task_tracking.h"
 #include "mojo/public/interfaces/bindings/interface_control_messages.mojom.h"
 
+{%- if use_wtf_types %}
+#include "mojo/public/cpp/bindings/lib/wtf_serialization.h"
+{%- endif %}
+
 {%- for namespace in namespaces_as_array %}
 namespace {{namespace}} {
 {%- endfor %}
 {%- if variant %}
 namespace {{variant}} {
 {%- endif %}
 
 {#--- Constants #}
 {%- for constant in module.constants %}
 {%-   if not constant.kind|is_integral_kind %}
@@ skipping 79 matching lines @@
 {%- endif %}
 {%- for namespace in namespaces_as_array|reverse %}
 }  // namespace {{namespace}}
 {%- endfor %}
 
 #if defined(__clang__)
 #pragma clang diagnostic pop
 #elif defined(_MSC_VER)
 #pragma warning(pop)
 #endif