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- Add hardware secure codecs and encryption_scheme support
- Use a vector for supported session types in case we need to support
  more session types in the future
- Use the mojom type directly on the client side to avoid duplicate code

Bug: 848532
Test: No functionality change.
Change-Id: Ieb61bdd223bc340593eb633b5f85e1abc3cec6f8
Reviewed-on: https://chromium-review.googlesource.com/1102836Reviewed-by: Nasko Oskov <nasko@chromium.org>
Reviewed-by: John Rummell <jrummell@chromium.org>
Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568237}