Allows to use camera portal separately in implementations where each
implementation needs to be called in different places.
This is targeted for Firefox support, where we need to ask for camera
access in the FF frontend code, otherwise making camera access requests
in the backend WebRTC code might result into presenting portal dialogs
asking for access from the javascript API.
Bug: webrtc:15202
Change-Id: Ida8b010bb93e08a9e5ddd9dd8a2a3549ee7fde8b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/305222
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Alexander Cooper <alcooper@chromium.org>
Commit-Queue: Jan Grulich <grulja@gmail.com>
Cr-Commit-Position: refs/heads/main@{#40148}
