Reland "Fix PDF OCR metrics."

This is a reland of commit 416f0319cd26755953a05abb770fa5c5825453d2

Original change's description:
> Fix PDF OCR metrics.
>
> 1- Prevents double recording of:
>     - 'Accessibility.PdfOcr.InaccessiblePdfPageCount'
>     - 'Accessibility.PdfOcr.ActiveWhenInaccessiblePdfOpened'
> 2- Records 'Accessibility.PdfOcr.InaccessiblePdfPageCount' for all
>    inaccessible PDFs regardless of PDF OCR being active or not.
>    This is changed to get a better coverage on distribution of
>    inaccessible PDFs.
>
> Since this feature is still in prelaunch phase, new UMA metrics are
> not added to replace the previous ones.
>
> AX-Relnotes: n/a
> Bug: 1443341
> Change-Id: I488dd4304bccb0df1609fd4baa88e0ab3c81b592
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4793749
> Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
> Reviewed-by: Kyungjun Lee <kyungjunlee@google.com>
> Reviewed-by: Evan Liu <evliu@google.com>
> Reviewed-by: Lei Zhang <thestig@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1186280}

Bug: 1443341
Change-Id: I8993af339450e26485fd9b194c13a933a0880827
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4801198
Reviewed-by: Evan Liu <evliu@google.com>
Auto-Submit: Ramin Halavati <rhalavati@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Kyungjun Lee <kyungjunlee@google.com>
Cr-Commit-Position: refs/heads/main@{#1186683}