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This CL adds mutator changes for adding the content indexed items.
The view holders will be added in a later CL.
1 - Comparator interface was changed to Sorter
2 - Prefetch tab will show a date wise sorted list which will have
    standalone prefetch cards and group cards for content indexing.
3 - Added CardPaginator to remember the pagination for each card
4 - Added GroupCardLabelAdder to add card header and footer
5-  Introduced dividers as separate view holders to handle top,
    middle, and bottom dividers in a group card.

Bug: 1030924
Change-Id: I033ce36344d3b7095a6b9a5e6d47e9b273121954
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1941041
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721835}