Mojo: Align string sizes when serializing a native type.

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

 size_t GetSerializedSize_(const {{struct.name}}Ptr& input,
                           mojo::internal::SerializationContext* context);
 void Serialize_({{struct.name}}Ptr input, mojo::internal::Buffer* buffer,
                 internal::{{struct.name}}_Data** output,
                 mojo::internal::SerializationContext* context);
 bool Deserialize_(internal::{{struct.name}}_Data* input,
                   {{struct.name}}Ptr* output,
                   mojo::internal::SerializationContext* context);
 
 {%- if struct|is_native_only_kind and struct|is_typemapped_kind %}
@@ skipping 82 matching lines @@
   static size_t GetSize(const NativeType& input) {
     size_t size = sizeof(internal::{{struct.name}}_Data);
 {%- for pf in struct.packed.packed_fields_in_ordinal_order %}
     do {
 {%-   if pf.field.kind|is_nullable_kind %}
       if (!mojo::StructTraits<{{struct.name}}, NativeType>
               ::has_{{pf.field.name}}(input))
         break;
 {%-   endif %}
 {%-   if pf.field.kind|is_string_kind %}
-      size += mojo::internal::String_Data::Traits::GetStorageSize(
-          static_cast<uint32_t>(mojo::StructTraits<{{struct.name}}, NativeType>
-              ::{{pf.field.name}}(input).size()));
+      size += mojo::internal::Align(
+          mojo::internal::String_Data::Traits::GetStorageSize(
+              static_cast<uint32_t>(
+                  mojo::StructTraits<{{struct.name}}, NativeType>
+                      ::{{pf.field.name}}(input).size())));
 {%-   elif pf.field.kind|is_object_kind %}
       NOTREACHED() << "Unsupported field type for StructTraits: "
                    << "{{pf.field.name}}";
 {%-   endif %}
     } while (false);
 {%- endfor %}
     return size;
   }
 
   static void Serialize(const NativeType& input,
@@ skipping 31 matching lines @@
 
   static bool Deserialize(internal::{{struct.name}}_Data* input,
                           NativeType* output,
                           mojo::internal::SerializationContext* context) {
     return mojo::StructTraits<{{struct.name}}, NativeType>::Read(
         {{struct.name}}_Reader(input, context), output);
   }
 };
 
 {%- endif %}  {# not variant #}