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* Adds support for tracking which domains trigger app banners.
  These metrics are split between native apps and web apps
  since developers are likely to prefer one over the other.

* Changes rappor.xml to have information about the new metrics.

BUG=458548

Review URL: https://codereview.chromium.org/939263002

Cr-Commit-Position: refs/heads/master@{#317158}