Add field-initializing constructors to generated mojo structs.

mojo/public/tools/bindings/generators/cpp_templates/wrapper_class_definition.tmpl

-// static
-{{struct.name}}Ptr {{struct.name}}::New() {
-  {{struct.name}}Ptr rv;
-  mojo::internal::StructHelper<{{struct.name}}>::Initialize(&rv);
-  return rv;
-}
-
-{{struct.name}}::{{struct.name}}()
-{%- for field in struct.fields %}
-    {% if loop.first %}:{% else %} {% endif %} {{field.name}}({{field|default_value}}){% if not loop.last %},{% endif %}
-{%- endfor %} {
-}
-
-{{struct.name}}::~{{struct.name}}() {
-}
+{% for constructor in struct|struct_constructors %}
+{{struct.name}}::{{struct.name}}(
+{%-  for field in constructor.params  %}
+{%-    set type = field.kind|cpp_wrapper_param_type %}
+{%-    set name = field.name %}
+    {{type}} {{name}}_in
+{%-    if not loop.last -%},{%- endif %}
+{%-  endfor %})
+{%-  for field, is_parameter in constructor.fields %}
+{%-    set name = field.name %}
+    {% if loop.first %}:{% else %} {% endif %} {{name}}(
+{%-    if is_parameter -%}
+std::move({{name}}_in)
+{%-    else -%}
+{{ field|default_value }}
+{%-    endif -%}
+){%  if not loop.last %},{% endif %}
+{%-  endfor %} {}
+{% endfor %}
+{{struct.name}}::~{{struct.name}}() = default;
 
 {%- if struct|is_hashable %}
 size_t {{struct.name}}::Hash(size_t seed) const {
 {%-   for field in struct.fields %}
 {%-     if for_blink %}
   seed = mojo::internal::WTFHash(seed, this->{{field.name}});
 {%-     else %}
   seed = mojo::internal::Hash(seed, this->{{field.name}});
 {%-     endif %}
 {%-   endfor %}
   return seed;
 }
 {%- endif %}