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This CL adds the UI for showing content indexed content.
1- Renames PrefetchViewHolder to PrefetchArticleViewHolder (and the XML files)
2- Adds separate view holders for prefetch grouped item, card header,
  card footer, and prefetch audio
3- Favicon will be added in a followup CL

Bug: 1030924
Change-Id: Ie95f8c1340423218652964b126d9bb09ac6237cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1929869
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721837}