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Update the CDM interface to provide information on the encryption scheme
and pattern necessary to decode the encrypted media. Currently only 'cenc'
decryption is supported. Detection (and support) of other schemes will be
done later.

Note that only CDMs that implement the ContentDecryptionModule_10 interface
will be able to use this information. CDMs that implement a previous version
of the interface will not get this information, so only 'cenc' encrypted
(or unencrypted) data will be passed to those CDMs.

BUG=658026
TEST=existing EME browser_tests pass

Change-Id: I14d7d1a44f0d7ff721dab7d6046a29a65055b3a4
Reviewed-on: https://chromium-review.googlesource.com/933730
Commit-Queue: John Rummell <jrummell@chromium.org>
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540985}