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This CL uses a rudimentary views::Label to display header text for
AutocompleteResults that contain matches with headers.

Screenshot: https://i.imgur.com/f61GxWR.png

Bug: 1052522
Change-Id: I042c21a60a8416e243498793cee5c3dabeaac4f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2137673
Commit-Queue: Tommy Li <tommycli@chromium.org>
Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756863}