Windows accessibility clients talk directly to the content process via COM.
In order to expose an OOP iframe document accessible as a child of the embedder iframe accessible via COM, the embedder process needs a COM proxy for the iframe document accessible.
This is exposed on the embedder's BrowserBridgeChild, so we can use this when a client asks for the child of the OuterDocAccessible.
Differential Revision: https://phabricator.services.mozilla.com/D32281
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extra : moz-landing-system : lando