media: Support GetStatusForPolicy() in pepper CDM

- Update PpapiDecryptor et al to support GetStatusForPolicy().
- Update PPP_CONTENT_DECRYPTOR_PRIVATE interface to support
  GetStatusForPolicy().
- Update PPB_CONTENT_DECRYPTOR_PRIVATE interface to support
  PromiseResolvedWithKeyStatus().
- Add PolicyCheck browser test.

In future CLs:
- GetStatusForPolicy() will also be supported in mojo CDM.
- Widevine CDM will be updated to support GetStatusForPolicy().

BUG=709348
TEST=New tests added

Change-Id: Ida71224a60bd4cbf9a37b9613c2fd84acb878f60
Reviewed-on: https://chromium-review.googlesource.com/576152
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: John Rummell <jrummell@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#489077}
35 files changed