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This CL changes NativeDesktopMediaList to no longer assume that
CaptureFrame completes synchronously. This means changing the code
to wait for OnCaptureResult before calling CaptureFrame again.

DCHECKs are added to DesktopCapturerLacros to guard against such
misuse in the future.

Bug: 1141483
Change-Id: I579dd0f5ea8bef9a02c7be6d3dead23805601038
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2492940
Commit-Queue: Darin Fisher <darin@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820483}