media: Add CdmSystemCode to enums.xml

This allows as to treat *SystemCode UMAs as enums. (They are reported as
sparse histograms.)

Change-Id: I41dac5917ea202fd6a11faa26a2e8fdb86eb78c0
Reviewed-on: https://chromium-review.googlesource.com/915011
Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536408}
2 files changed