GitLab

Add support for load/remove persistent license at Android level.

Load:
1. Load eme session ID to key set ID map from persistent storage.
2. MediaDrm.restoreKeys.

Remove:
1. Generate key release request.
2. Update session with key release response.
3. Clear persistent storage.

BUG=493521
TEST=test page

Review-Url: https://codereview.chromium.org/2796843002
Cr-Commit-Position: refs/heads/master@{#462690}