I've started working on this. Assign to myself.

hmchen: As discussed offline in the email thread, we should use x-cdm* for CDM specific fields in the manifest.json file. Also, "offline" is not accurate, we should stick with spec terms. So how about replacing "offline_enabled" with "x-cdm-persistent-license-support" in the manifest.json file?

Note that in issue 469202, we proposed to have

"x-cdm-media-key-session-types": "temporary,persistent-usage-record,persistent-license",

or 

"x-cdm-media-key-session-types": [
  "temporary",
  "persistent-usage-record",
  "persistent-license"
]

Given it's reasonable to assume "temporary" session is always supported, "persistent-usage-record" is not in the current spec. I feel just have a boolean would make things simpler and safer (to parse).

Changing to "x-cdm-persistent-license-support" should be easy. I remember Thomas mentioned "offline" may be already used by some partners. So, I cc'ed Thomas. We can also discuss this in today's meeting.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e722a50fc9d677c6db5f146a689e79ceba1d1142

commit e722a50fc9d677c6db5f146a689e79ceba1d1142
Author: Xiaohan Wang <xhwang@chromium.org>
Date: Tue Oct 17 09:14:34 2017

media: Add test for persistent license support

This CL updates EncryptedMediaSupportedTypesTest (and related tests
classes) to test persistent license support.

BUG= 767941 
TEST=Add new test cases

Change-Id: Iece24005316ce1e4f09cd807756499d69e4c7821
Reviewed-on: https://chromium-review.googlesource.com/719384
Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Reviewed-by: John Rummell <jrummell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509332}
[modify] https://crrev.com/e722a50fc9d677c6db5f146a689e79ceba1d1142/chrome/browser/media/encrypted_media_supported_types_browsertest.cc
[modify] https://crrev.com/e722a50fc9d677c6db5f146a689e79ceba1d1142/media/test/data/test_key_system_instantiation.html

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cd4e1cff8bd01bf4524d60637486bdee2fa4bac5

commit cd4e1cff8bd01bf4524d60637486bdee2fa4bac5
Author: Xiaohan Wang <xhwang@chromium.org>
Date: Tue Oct 17 19:58:19 2017

media: Get CDM persistent-license support info from manifest.json

- Read the value of "x-cdm-persistent-license-support" from the CDM
  manifest.json file.
- Push this info into WebPluginMimeType additional_param_names and
  additional_param_values when registering the CDM.
- In the renderer process, when registering Widvine key system, read the
  info from additional_param_names and additional_param_values.
- On Linux/ChromeOS, this info is not read from the manifest.json file.
  Rather, it's hard-coded in chrome_content_client.cc. We should
  update this in a future CL once we check in CDMs that supports
  persistent-license. Ultimately we will support component CDM on Linux
  and ChromeOS the CDM registration code will be removed from
  chrome_content_client.cc altogether.

In future CLs, we will implement key system support using CdmRegistry
instead of using WebPluginMimeType. Then we can abandon all the code
related to WebPluginMimeType additional_param_names and
additional_param_values.

BUG= 767941 
TEST=Manually tested on Windows.

Change-Id: Ic9f3ec3ce0f454e170623165f9f046c7e6f0885a
Reviewed-on: https://chromium-review.googlesource.com/719379
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: John Rummell <jrummell@chromium.org>
Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509493}
[modify] https://crrev.com/cd4e1cff8bd01bf4524d60637486bdee2fa4bac5/chrome/browser/component_updater/widevine_cdm_component_installer.cc
[modify] https://crrev.com/cd4e1cff8bd01bf4524d60637486bdee2fa4bac5/chrome/common/chrome_content_client.cc
[modify] https://crrev.com/cd4e1cff8bd01bf4524d60637486bdee2fa4bac5/chrome/renderer/media/chrome_key_systems.cc
[modify] https://crrev.com/cd4e1cff8bd01bf4524d60637486bdee2fa4bac5/third_party/widevine/cdm/widevine_cdm_common.h