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This is a reland of cf071719

Original change's description:
> [Accessibility] Volume slider reads out level in percentages.
>
> This CL makes it such that the volume level is read out as a percentage
> in aria. This CL also amplifies how the accessibility information is
> given to aria, by setting attributes instead of explicitly creating
> accessibility nodes.
>
> Bug: 905024
> Change-Id: I0ee5a91215669f39c7394d3c8f113ae83a74cf00
> Reviewed-on: https://chromium-review.googlesource.com/c/1337298
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
> Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
> Commit-Queue: CJ DiMeglio <lethalantidote@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#612160}

TBR=mlamouri@chromium.org, dmazzoni@chromium.org, thakis@chromium.org

Bug: 905024
Change-Id: Ie35c05c274dfd36f3e9ec0a32b587a98a62249d9
Reviewed-on: https://chromium-review.googlesource.com/c/1356007Reviewed-by: CJ DiMeglio <lethalantidote@chromium.org>
Commit-Queue: CJ DiMeglio <lethalantidote@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612469}