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This is a reland of ebc60412

Original change's description:
> [omnibox] Fix ZeroSuggestProvider duplicate classifications bug
> 
> The below CL introduces a bug, where ZeroSuggestProvider can create
> a match with duplicate text classifications. This triggers a DCHECK
> as described in the linked bug.
> 
> https://chromium-review.googlesource.com/c/chromium/src/+/1947765
> 
> This CL fixes it and adds a test.
> 
> Bug: 1030741
> Change-Id: If59fbd320d720e2a7ff8d2f66d9ee92e11bb9a68
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1951557
> Commit-Queue: Tommy Li <tommycli@chromium.org>
> Reviewed-by: manuk hovanesian <manukh@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#722497}

Bug: 1030741
Change-Id: Ic169c05bfc953da56b161beb677e454ad0b2d437
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1955787Reviewed-by: manuk hovanesian <manukh@chromium.org>
Commit-Queue: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#722573}