[manifest] Issue a developer warning if the display mode is not a known value. (#286)

Fixes issue 283.
You can merge this Pull Request by running:

  git pull https://github.com/mounirlamouri/manifest display_warning

Or you can view, comment on it, or merge it online at:

  https://github.com/w3c/manifest/pull/286

-- Commit Summary --

  * Issue a developer warning if the display mode is not a known value.

-- File Changes --

    M index.html (6)

-- Patch Links --

https://github.com/w3c/manifest/pull/286.patch
https://github.com/w3c/manifest/pull/286.diff

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/manifest/pull/286