Fix new html_extra_path option for singlehtml builder.

sphinx/builders/html.py

@@ -974,6 +974,7 @@ class SingleFileHTMLBuilder(StandaloneHTMLBuilder):
         self.copy_image_files()
         self.copy_download_files()
         self.copy_static_files()
+        self.copy_extra_files()
         self.write_buildinfo()
         self.dump_inventory()
 

tests/test_build_html.py

@@ -363,4 +363,3 @@ def test_html_with_globaltoc_and_hidden_toctree(app):
             '\n   :hidden:'
             '\n')
     app.builder.build_all()
-