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- Autogenerate Polymer 3 version of managed-footnote and tests
- Add to demo page
- Add new build targets and browser test files as needed since this is
the first CrComponent to be ported.
- Also adding a way for the TestDataSource to serve an empty version
of strings.m.js, for tests that need to override values in loadTimeData

Bug: 965770
Change-Id: Id8ce7b102c8cb86d84e606a6bc9046cecd6f284c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1809747Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697748}