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

mojo/public/tools/bindings/generators/cpp_templates/module.h.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 14 matching lines @@
 #include "mojo/public/cpp/bindings/associated_interface_request.h"
 #include "mojo/public/cpp/bindings/callback.h"
 #include "mojo/public/cpp/bindings/interface_ptr.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "mojo/public/cpp/bindings/lib/control_message_handler.h"
 #include "mojo/public/cpp/bindings/lib/control_message_proxy.h"
 #include "mojo/public/cpp/bindings/lib/serialization.h"
 #include "mojo/public/cpp/bindings/map.h"
 #include "mojo/public/cpp/bindings/message_filter.h"
 #include "mojo/public/cpp/bindings/no_interface.h"
-#include "mojo/public/cpp/bindings/string.h"
 #include "mojo/public/cpp/bindings/struct_ptr.h"
 #include "mojo/public/cpp/bindings/struct_traits.h"
 #include "{{variant_path}}-internal.h"
 {%- for import in imports %}
 #include "{{import.module.path}}.h"
 {%- endfor %}
 {%- if variant %}
 #include "{{module.path}}.h"
 {%- endif %}
+{%- if not use_wtf_types %}
+#include "mojo/public/cpp/bindings/string.h"
+{%- else %}
+#include "third_party/WebKit/Source/wtf/text/WTFString.h"
+{%- endif %}
 
 {%- for namespace in namespaces_as_array %}
 namespace {{namespace}} {
 {%- endfor %}
 {%- if variant %}
 namespace {{variant}} {
 {%- endif %}
 
 {#--- Enums #}
 {% from "enum_macros.tmpl" import enum_decl -%}
@@ skipping 128 matching lines @@
 {%- endfor %}
 
 {%- if variant %}
 }  // namespace {{variant}}
 {%- endif %}
 {%- for namespace in namespaces_as_array|reverse %}
 }  // namespace {{namespace}}
 {%- endfor %}
 
 #endif  // {{header_guard}}