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This is a reland of b02a397f

This includes the missing deps that caused the component builds to fail
and EXPORTs the AccessibilityBridge class for testing.

Original change's description:
> [fuchsia] Register Views with Fuchsia Accessibility APIs
>
> * Add the AccessibilityBridge class skeleton, which will eventually
> handle the logic for conversion between Chromium and Fuchsia
> accessibility data structures.
> * Register a ViewRef to the Fuchsia SemanticsManager.
>
> Test: Added AccessibilityBridgeUnitTest.*
>
> Bug: 973095
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1708043
> Commit-Queue: Sharon Yang <yangsharon@chromium.org>
> Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
> Reviewed-by: Wez <wez@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#693914}

Bug: 973095
Change-Id: I3a5a958fc88a5804023372453420863e97f9df74
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1792460Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Sharon Yang <yangsharon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695013}