Add type annotations to gallery/js/ribbon.js.

BUG=406995
TEST=GYP_GENERATORS=ninja tools/gyp/gyp --depth . ui/file_manager/gallery/js/compiled_resources.gyp && ninja -C out/Default | grep "ribbon.js" -2

Review URL: https://codereview.chromium.org/719273004

Cr-Commit-Position: refs/heads/master@{#304158}
1 file changed