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This CL implements the CameraPrivacySwitchObserver on Chrome side and
provide an interface in CameraHalDispatcherImpl to let other components
in Chrome to add observers for camera privacy switch status changed.

Bug: b/167994459
Test: Build successfully
Change-Id: I4efe132cd2d0a5988a4ffeb99ab0ca2802ad2a63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2551882
Commit-Queue: Wei Lee <wtlee@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Shik Chen <shik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836521}