GitLab

- Autogenerate Polymer 3 versions for files in on_startup_page/*
- Update closure compiler and polymer_modulizer/js_modulizer targets
  for these files
- Autogenerate tests for the Polymer 3 files

Bug: 1026426
Change-Id: I122bcb77d366b7fc7fd979b235d13d283faf8d43
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2040626
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739259}