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* Create a new skeleton InfoBarDelegate for app banners containing
  information about apps defined by web manifests.

* Displays an infobar when the user navigates to a page
  with a manifest.

* Adds a string for "Add to homescreen" for the new infobar.

BUG=453170

Review URL: https://codereview.chromium.org/893073002

Cr-Commit-Position: refs/heads/master@{#314273}