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Now we have CastAudioManagerAndroid. Move android specific logics into
the new class.

Bug: internel b/160753974
Test: Build
Change-Id: I9a3a177f938da525e8f18df3ee0be5588bdd6eb0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2337539Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Commit-Queue: Yuchen Liu <yucliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#794803}