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This adds a few things to the VaapiVideoDecoder for
protected content.
-Accepts encrypted/CDM configurations in Initialize
-Registers a callback with the CDM to get notified
 when new decryptions keys are available
-When in protected mode, configures VaapiWrapper that way
-Adds a new kWaitingForProtected state when it is waiting
 for keys, hw config, full sample decryption.
-Callback to be used by accelerators to notify when
 protected decode should resume

BUG=b:153111783,b:155509236
TEST=Builds, protected playback works w/ full set of changes

Change-Id: Ibd52ddd90af732d5ae736989c2008f4f4fdcd38f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2535578
Commit-Queue: Jeffrey Kardatzke <jkardatzke@google.com>
Reviewed-by: Jao-ke Chin-Lee <jchinlee@chromium.org>
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829083}