The Storage ID will be used bind offline licenses to the device they are
issued for. It needs to be unique per browser, per device, per origin,
and per profile.
The following values are combined:
- CDM storage key id (to distinguish browsers)
- Preference media.storage_id_salt
- current page's origin
- device identification (varies by platform)

Creation of the Storage ID is determined by the GN flag
$enable_cdm_storage_id. The default value is to only generate the
value on chrome builds on supported platforms, but can be overridden
for testing.

BUG=478960
TEST=Storage ID browser_tests pass

Change-Id: I10d8b897c44c633bf6ddcc35d965ed3c21d481c8
Reviewed-on: https://chromium-review.googlesource.com/729266


Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510665}