media: Add HDCP policy check on MediaKeys (chromium)

This API provides an API for JS application to check the key status
associated with a policy without the need to fetch an actual license.
This is critical for starting playback at higher resolution and hence a
better user experience.

This CL updates the Chromium side to support the new API:
- Convert the HDCP version string to enum.
- Pass the call down to media::ContentDecryptionModule.

By default CDMs do not support this call (rejecting the promise). In
future CLs it will be enabled in CDMs that do support it.

BUG=709348

Change-Id: I55dd05060013464cc9660e5d8365c6adeace6630
Reviewed-on: https://chromium-review.googlesource.com/541776
Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: John Rummell <jrummell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485672}
12 files changed