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Add the HorizontalReorderingLayout, which is the layout of the thumb
strip when reordering cells while the DragAndDrop flag is disabled.

Add a set of helper functions to be called by both the
HorizontalReorderingLayout and the GridReorderingLayout.

Change-Id: Id0b475c7e9cb97c537ce3b30d3936d0c82d1f2cf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2462125Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: Roberto Moura <mouraroberto@google.com>
Auto-Submit: Roberto Moura <mouraroberto@google.com>
Cr-Commit-Position: refs/heads/master@{#816775}