SDK / exoplayer

Apps targeting API 28 by default do not grant permission for cleartext traffic,
so update the demo app to show a warning if loading an HTTP URI will fail. See
https://developer.android.com/about/versions/pie/android-9.0-changes-28 for
information on behavior changes in API 28.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=208204937